Typo:

since I but the XPS 8700

Should have been:

since I bought the XPS 8700

More info from the Windows troubleshooter:

PrintWindows Network Diagnostics Publisher details

Issues found
Problem with wireless adapter or access point

Problem with wireless adapter or access point Not fixed Not Fixed
Reset the wireless adapter Completed
Investigate router or access point issues Completed

Issues found Detection details

5 Problem with wireless adapter or access point Not fixed Not Fixed

Reset the wireless adapter Completed

InformationalNetwork Diagnostics Log
File Name: 20AA096C-04BF-4F89-A11F-35D774388EDE.Repair.1.etl Detection details Expand

InformationalDiagnostics Information (Network Adapter)
Details about network adapter diagnosis:

Network adapter Wi-Fi driver information:

Description . . . . . . . . . . : Dell Wireless 1704 802.11b/g/n (2.4GHz)
Manufacturer . . . . . . . . . : Broadcom
Provider . . . . . . . . . . . : Broadcom
Version . . . . . . . . . . . : 7.35.295.0
Inf File Name . . . . . . . . . : C:\WINDOWS\INF\oem14.inf
Inf File Date . . . . . . . . . : Monday, August 3, 2015 6:17:14 PM
Section Name . . . . . . . . . : BCM43XNG_NT64
Hardware ID . . . . . . . . . . : pci\ven_14e4&dev_4365&subsys_00161028
Instance Status Flags . . . . . : 0x180200a
Device Manager Status Code . . : 0
IfType . . . . . . . . . . . . : 71
Physical Media Type . . . . . . : 9

InformationalDiagnostics Information (Wireless Connectivity)
Details about wireless connectivity diagnosis:

Information for connection being diagnosed
Interface GUID: 524572c2-34b1-4002-9972-59160f5e57bf
Interface name: Dell Wireless 1704 802.11b/g/n (2.4GHz)
Interface type: Native WiFi

Connection incident diagnosed
Auto Configuration ID: 7
Connection ID: 7

Connection status summary
Connection started at: 2015-08-31 06:12:32-989
Profile match: Success
Pre-Association: Success
Association: Success
Security and Authentication: Fail

List of visible access point(s): 7 item(s) total, 7 item(s) displayed
BSSID BSS Type PHY Signal(dB) Chnl/freq SSID
-------------------------------------------------------------------------
[Apparently tried to connect via all available wireless signals - I do not list them here for privacy reasons (not sure if it matters, but I don't want to take the risk.]

Connection History

Information for Auto Configuration ID 7

List of visible networks: 7 item(s) total, 7 item(s) displayed
BSS Type PHY Security Signal(RSSI) Compatible SSID
------------------------------------------------------------------------------

Infra Yes 64 Yes [my wireless name]

List of preferred networks: 4 item(s)
Profile: [my wireless name]
SSID: [my wireless name]
SSID length: 18
Connection mode: Infra
Security: Yes
Set by group policy: No
Connect even if network is not broadcasting: No
Connectable: Yes
Profile: mdwpsyd's iPhone
SSID: mdwpsyd's iPhone
SSID length: 16
Connection mode: Infra
Security: No
Set by group policy: No
Connect even if network is not broadcasting: No
Connectable: No
Reason: 0x00028003

Information for Connection ID 7
Connection started at: 2015-08-31 06:12:32-989
Auto Configuration ID: 7
Profile: [my wireless name]
SSID: [my wireless name]
SSID length: 18
Connection mode: Infra
Security: Yes
Pre-Association and Association
Connectivity settings provided by hardware manufacturer (IHV): No
Security settings provided by hardware manufacturer (IHV): No
Profile matches network requirements: Success
Pre-association status: Success
Association status: Success
Last AP: 6c-b0-ce-ad-24-1a
Security and Authentication
Configured security type: WPA2-PSK
Configured encryption type: CCMP(AES)
802.1X protocol: No
Key exchange initiated: Yes
Unicast key received: No
Multicast key received: No
Number of security packets received: 0
Number of security packets sent: 0
Security attempt status: Fail 0x00048005

Information for Auto Configuration ID 6

List of visible networks: 7 item(s) total, 7 item(s) displayed
BSS Type PHY Security Signal(RSSI) Compatible SSID
------------------------------------------------------------------------------
Infra Yes 60 Yes [my wireless name]

List of preferred networks: 4 item(s)
Profile: [my wireless name]
SSID: [my wireless name]
SSID length: 18
Connection mode: Infra
Security: Yes
Set by group policy: No
Connect even if network is not broadcasting: No
Connectable: No
Reason: 0x00028006
Profile: mdwpsyd's iPhone
SSID: mdwpsyd's iPhone
SSID length: 16
Connection mode: Infra
Security: No
Set by group policy: No
Connect even if network is not broadcasting: No
Connectable: No
Reason: 0x00028002

Information for Connection ID 6
Connection started at: 2015-08-31 06:11:27-378
Auto Configuration ID: 6
Profile: [my wireless name]
SSID: [my wireless name]
SSID length: 18
Connection mode: Infra
Security: Yes
Pre-Association and Association
Connectivity settings provided by hardware manufacturer (IHV): No
Security settings provided by hardware manufacturer (IHV): No
Profile matches network requirements: Success
Pre-association status: Success
Association status: Success
Last AP: 6c-b0-ce-ad-24-1a
Security and Authentication
Configured security type: WPA2-PSK
Configured encryption type: CCMP(AES)
802.1X protocol: No
Key exchange initiated: Yes
Unicast key received: No
Multicast key received: No
Number of security packets received: 0
Number of security packets sent: 0
Security attempt status: Fail 0x00048005

Information for Auto Configuration ID 5

List of visible networks: 7 item(s) total, 7 item(s) displayed
BSS Type PHY Security Signal(RSSI) Compatible SSID
------------------------------------------------------------------------------
Infra Yes 38 Yes [my wireless name]

List of preferred networks: 4 item(s)
Profile: [my wireless name]
SSID: [my wireless name]
SSID length: 18
Connection mode: Infra
Security: Yes
Set by group policy: No
Connect even if network is not broadcasting: No
Connectable: No
Reason: 0x00028006

Information for Connection ID 5
Connection started at: 2015-08-31 06:10:21-712
Auto Configuration ID: 5
Profile: [my wireless name]
SSID: [my wireless name]
SSID length: 18
Connection mode: Infra
Security: Yes
Pre-Association and Association
Connectivity settings provided by hardware manufacturer (IHV): No
Security settings provided by hardware manufacturer (IHV): No
Profile matches network requirements: Success
Pre-association status: Success
Association status: Success
Last AP: 6c-b0-ce-ad-24-1a
Security and Authentication
Configured security type: WPA2-PSK
Configured encryption type: CCMP(AES)
802.1X protocol: No
Key exchange initiated: Yes
Unicast key received: No


InformationalDiagnostics Information (Wireless Connectivity)
Details about wireless connectivity diagnosis:

For complete information about this session see the wireless connectivity information event.

Helper Class: Auto Configuration
Initialize status: Success

Information for connection being diagnosed
Interface GUID: 524572c2-34b1-4002-9972-59160f5e57bf
Interface name: Dell Wireless 1704 802.11b/g/n (2.4GHz)
Interface type: Native WiFi

Result of diagnosis: Problem found
Issue referred to: L2Sec Helper Class

Root cause:
Windows could not connect to "MyCharterWiFi1a-2G"
You can try to connect again.

Repair option:
Resetting your wireless network adapter
This will disable and then enable the network adapter "Wi-Fi" on this computer.

InformationalDiagnostics Information (L2sec Helper Class)
Details about L2Sec Helper Class diagnosis:

For complete information about this session see the Wireless Diagnostic Informational Event.

Helper Class: Layer2 Security
Initialize Status: Success

Result of diagnosis: Problem found

Root cause:
Windows cannot connect to "MyCharterWiFi1a-2G"
The wireless network security key is not correct.

Detailed root cause:
Layer 2 security key exchange using user-supplied key did not generate unicast keys before timeout

Repair option:
Verify the network security key for "MyCharterWiFi1a-2G"
View the security settings. You can then type the correct security key.

Information for connection being diagnosed
Interface GUID: {524572c2-34b1-4002-9972-59160f5e57bf}
Interface name: Dell Wireless 1704 802.11b/g/n (2.4GHz)
Interface type: Native WiFi
Profile: [my wireless name]
SSID: [my wireless name]
SSID length: 18
Connection mode: Infra
Security enabled: Yes
Connection ID: 7
Security settings provided by hardware manufacturer (IHV): No
Profile matches network requirements: Yes
Pre-Association and association status: Success
Security and Authentication:
Configured security type: Robust Secure Network (RSN / WPA2) for independent networks
Configured Encryption type: CCMP (AES)
Security connect status: Fail 0x00048005
Number of security packets received: 0
Number of security packets sent: 0
802.1X protocol: No
Key exchange initiated: Yes
Unicast keys received: No
Multicast keys received: No

InformationalNetwork Diagnostics Log
File Name: 20AA096C-04BF-4F89-A11F-35D774388EDE.Diagnose.0.etl

InformationalOther Networking Configuration and Logs
File Name: NetworkConfiguration.cab

Collection information
Computer Name: [my computer's name] 
Windows Version: 10.0
Architecture: x64
Time: Monday, August 31, 2015 6:12:43 AM

Publisher details Expand

Windows Network Diagnostics
Detects problems with network connectivity.
Package Version: 3.0
Publisher: Microsoft Windows

I can hardly believe it, but I solved it. 

The clue was in that long printout from the Windows troubleshooter:

Windows cannot connect to "[my WiFi name]"
The wireless network security key is not correct.

I spent a lot of time trying to figure out how to correct the network security key. Somewhere along the line, I figured I would uninstall the network adapter. I had reverted to the previous version, and when that didn't work, updated it, but I realized I had never uninstalled it. 

It took me a while to figure out how to reinstall it. Eventually, I used the Dell process of detecting my computer and then telling me which drivers were recommended for my system.

I installed two of the top 3 - one of them, an Intel driver, would not install. I am pretty sure this is the one that fixed the problem:

BCM_Wireless_WT4_D3P4M_A01_Setup_ZPE (1).exe

I did have to reboot, and then I right-clicked on the WiFi icon in the system tray, selected my WiFi, clicked "Connect", and then it asked me for my network security key. Fortunately, my ISP, which provided the router, makes it easy to find the security key (sticker on the router). I typed it in, and lo and behold, I had WiFi again. 

I sure hope Microsoft fixes this problem so that more people do not have to spend nearly 14 hours searching for a solution!

I think that was a second copy of the driver, so it will probably be listed as:

BCM_Wireless_WT4_D3P4M_A01_Setup_ZPE.exe

Update:

After reviewing my notes, it might have been the following two driver updates that helped. These driver updates are specific to XPS 8700, but I imagine there similar updates for other Dell desktops, laptops, etc. Dell made it much easier with the System Detect tool. 

BCM_Wireless_WT4_D3P4M_A01_Setup_ZPE
Windows 10, 64-bit
Driver and description: This package provides Dell DW1704 802.11 b/g/n Driver and is supported on XPS 8700 running the following Windows Operating systems: Windows 10.
Download URL: www.dell.com/.../DriversDetails;fileid=3479174503
Criticality:Recommended
Release date:8/13/2015 7:54:10 AM

8700_Network_Driver_HV7H1_WN32_18.11.0_A00
Driver and description: This package provides Intel 7260 WiFi Driver and is supported on XPS 8700 running the following Windows Operating systems: Windows 10.
Download URL: www.dell.com/.../DriversDetails;fileid=3475171474
Criticality:Recommended
Release date:7/29/2015 3:10:01 AM

I also highly recommend subscribing (via email or RSS) to Dell Technical Updates. They are almost a secret (not on purpose) as it is hard to find the "how to subscribe" info by searching the Dell website. That link will take you to the right web page though. 

~ Mark

I have Dell Inspiron 14Z. I had windows 8.1 but upgraded to Windows 10. After the upgrade, the wi-fi gets disconnected all the time. I have to restart my computer for the Wi-Fi to work again. Sometimes, the Wi-Fi works by simply using the troubleshoot problems option available after right clicking on the Wi-Fi icon. This is not a good thing. All my other devices - iPhone, iPad, MacBook Air connect to Wi-Fi without any issue.

I uninstalled the Wi-Fi driver and re-installed but the problem persists. Does Dell Support have any suggestions? I could not find any solutions from Microsoft support forums.

Network Adapter for Wi-Fi is Intel(R) Centrino(R) Wireless-N 2230, Driver Version 15.18.0.1

I was having a similar problem.  I updated the drivers, which didn't resolve it. 

What appears to have resolved it was going into the configuration of the WiFi adapter and clearing the checkbox allowing the computer to turn off the device to save power. 

I tried the option but I was getting wi-fi disconnected all the time. 

Had similar problems on a new Dell 8700 but also on a XPS 13.

The 8700 was finally fixed by following step 6 from Microsoft to purge all the network drivers:

windows.microsoft.com/.../fix-network-connection-issues

There are a number of network drivers installed now that weren't there previously.

Mike

Well, this is the common problem faced by the user after updating to Windows 10. And the issues might occur if the older VPN software is installed on Windows 8.1 and is present during the upgrade to Windows 10. Older software versions contain a Filter Driver (the Deterministic Network Enhancer) which is not properly upgraded, leads the issue.

However to fix the Wi-fi issues make use of the given solution

Solution 1: Verify VPN Option:

Step-1: Right-click on Start button and select Command Prompt (Admin) from the drop-down menu and launch Command Prompt as Admin.

Step-2: Enter the given command and then press Enter

reg delete HKCRCLSID{988248f3-a1ad-49bf-9170-676cbbc36ba3} /va /f

Step-3: Now enter the given command and press Enter

netcfg -v -u dni_dne

And restart your PC and check the Wi-Fi settings. You should now be able to get all visible networks around.

Hope this works.

You can read this article to get more information: www.reimagerepair.us.com/.../fix-wi-fi-stopped-working-after-updating-windows-10

That key doesn't exist on my computer.  My previous attempt to fix was only temporary.  The only fix has been to disable the Dell WiFi adapter and use a Netgear 802.11ac USB adapter in its place.

Change encryption type: CCMP(AES) to TKIP from your router settings and you'll see magic (solution).... haha.

Sorry for my english

I Made a nice detailed post but login failed and cleared the info - thanks for that.

Summary:

Try Windows System Restore, if that fails insert System Repair Disk and reboot, select repair option. These are the only things that I've found to work. Hopefully somebody smarter can enlighten us as to the real cause. I'm sure it's Windows 10 Update.

Good Luck