100% Disk usage

Mention your Capacity of RAM, Disk and occupied capacity of both to suggest fixes.

4GB RAM hdd is of 1 TB it is 75 % free

I am facing too.  Have done everything but not yet solved.

I have done clean install of windows 10 and now my problem is sloved you can also try it but first take your data backup

Try the below method and see if it makes any difference.

Disable or Delay Start the Windows Services

If you seldom use such Windows services, it is better to disable them and fix the 100% disk usage.
1. Use Windows shortcut keys Win + R to launch Run.
2. Type services.msc and press the Enter.
3. Locate to the Superfetch.
4. Double click the Superfetch service for Properties.
5. Select Automatic (Delay Start) from the drop-down menu of Startup type.
6. Double click the HomeGroup Listener, the HomeGroup Provider and the Windows Search.

Select Disable from the drop-down menu of Startup type.

I am facing the same issue and tried the above steps but still the problem exists. Mine is also 4 GB Ram and 1 TB hard disk with 70% free space. I have disabled the superfetch and prefetch services. Stopped the windows update service too. This 100% disk usage is causing system slowness.

I had this problem for quite some time. After trying many things, what I think solved it was:

1) Fix the Windows Update program

2) Fix the Dell Update program

Google to find out how.

MOST IMPORTANT :  KEEP THE LATEST WINDOWS UPDATES INSTALLED, IF YOUR MACHINE IS NOT RUNNING LATEST WINDOWS UPDATES THAN THIS ISSUE WILL NOT BE PERMANENTLY FIXED. 

Additionally you can make following changes. 

1. Run > MSCONFIG >> Services 

Uncheck these services and reboot

Background Intelligent Transfer Service 

Connected User Experiences and Telemetry

SysMain 

2 Run >> REGEDIT 

HKEY_LOCAL_MACHINE : Software : Policies >> Microsoft >> Windows>> data Collection  

On the right side do a right Click > New : DWORD (32 bit) and name it to “Allow Telemetry” 

HKEY_LOCAL_MACHINE  >> System CurrentControl Set  >> Services >>>> TimeBrokerSvc >> On the right-hand side change the value of the “Start” to 4 

HKEY_LOCAL_MACHINE >> System >> CurrentControl Set >> Control >> Session Manager >> Click on Memory Management >> Change the Value of “ClearPageFileAtShutdown to 1 

Go to settings > privacy > diagnostics and feedback > Optional 

Settings > System > Notifications > Turn every notification off 

Setting > Privacy  > Background apps > Turn off 

Reboot 

Once again having latest windows update is must. Please check your windows build by Run > Winver 

If you get any number like 2004 or below, you are running an old build and you should update your windows, by running Microsoft Upgrade assistance application. 

I'm sure you found the solution by now, but I came across the same issue and found that if I run Services.msc and stopped the dell services it fixed the issue.  The service I ended up turning off/disabled was the dell service linked to installing software.  Once I turned that off it HDD usage dropped back to normal.

Anyone still struggling with 100% disk utilization in your Dell Laptop (mine is Inspiron 15 5000 series), do yourself a HUGE favor -- and save yourself countless hours of frustration and wasted time -- and replace your HDD with an SDD.  That's it.  Done. Problem solved.  I bought a 2.5" 1TB Micron Crucial SDD (Product SKU:CT1000MX500SSD1, Product Name::Crucial MX500 1000GB 2.5 inch SSD) for $69.99 as of this writing.  You'll also need to buy a SATA to USB 3.0 Adapter cable.  I got one from an online store for $3.18 with free shipping.  You'll also want to buy a 16GB or 32GB USB just to make sure you have a Windows recovery drive in case something goes horribly wrong (luckily I didn't need it).  I found a 2-pack of 32GB USB sticks for $9.28 incl tax and free shipping.  The downloadable software from the Micron/Crucial site allows you to create an exact duplicate of your HDD onto the new SDD.  There are numerous online videos showing how to do the HDD removal and replacement.  I am barely above novice level when it comes to computers and I did it, so you can too.  My system is 10,000% better. Boots in less than 30 seconds and then give it another 10-15 seconds for things to settle down after I've entered my passcode and then I'm off and running. Total game changer.