I was able to fix my computer. I went to this dell support page. Typed in my computer model. Ran diagnostic tests. Looked for driver updates. One was listed for my network card. No driver updates were given going through the windows 10 settings update utility. Here is the page I went to. Product Support | Dell US good luck.

I found it in the manual update section.

I have been having the same problem. It has happened 3 times now. It will go away and then it will return at a later date. Lost it about a week ago again. It has still not returned. My situation is exactly as you have explained above. 

@Gary3072   - Dell doesn't support Win 10 on the  Studio XPS 7100. So exactly what driver did you try to install since there's no Win 10 driver? The only BT driver I see for the Studio XPS 7100 is for Win 7, which won't work with Win 10.

Try this:
Open Device Manager and click View>Show hidden devices on the DM toolbar. Then go down the entire list in DM looking or any "Unknown" devices. Right-click and uninstall all Unknown devices. Next, click Action>Scan for hardware changes and see if the correct driver gets installed and BT works again.

NOTE: you may have to reboot after the driver gets installed before BT starts working again...

I replaced motherboard and battery in 2018... should be okay. 

Yea i dont see anything that says "unknown" in the DM 

@Gary3072  -  If no Unknown is listed, just try scanning for new hardware. If an Unknown appears after scanning, uninstall it.

If that doesn't help, when was last time you replaced the motherboard battery? BIOS may have lost track of the BT module if that battery is weak/dead so...

1. Reboot and start tapping F2 when you see the Dell splash screen to open BIOS setup
2. Copy down all current BIOS settings, to be safe
3. Power off, unplug
4. Press/hold power button for ~15 sec
5. Open case and remove motherboard battery (check Service Manual for details)
6. Press/hold power button for ~30 sec
7. Install fresh CR2032 3-volt coin cell battery (~$2)
8. Close up and connect mouse, monitor and keyboard
9. Reboot and see if BT works now...

And I guess it's always possible the BT module simply died...

Forgot to mention I’m not using WiFi, just Ethernet. Does that have anything to do with the Bluetooth not showing? 

These days 3 years is a long time for motherboard batteries. I'd still clear BIOS even if you don't want to replace the battery.

Using Ethernet should not have any relationship to your BT issue. The Bluetooth module in the Studio XPS 7100 is separate from any WiFi card you may have. The Service Manual doesn't even mention a WiFi card, and the specs say WiFi is optional.

The driver for the WiFi card that Dell installed in this PC model calls it an "Atheros Wireless 1525 WLAN Mini Card" which means it's a PCI-e card, and makes no mention of BT. So it must be separate from the BT module.

If all else fails, you could replace the BT card, which I see for ~$10, used. Instructions are in the Service Manual to remove the BT module, and I presume the card can be swapped in the module, if you're willing/capable of doing it.

Or, just get a USB>BT dongle and plug that into an available USB2 port.

Good choice!

Post back and let us know which dongle you get and if it meets your expectations...