w10 or w7 loaded. nobody can guess any OS. if you force them to answers many will be wrong BIG TIME.

wireless keyboards acting odd is bad battery in same. (like millions have right now world wide,.. endless)

The BT wifi card can not scan any dead keyboard ever, over BT. battery dead

if the driver is bad reload it.

here is the order of failures... generic. I dont have full spec on any of these  and most OEMs docs stinks here.

• battery dead inside keyboard, #1 all time most likely.
• USB port dead or stuck in sleep mode,  bad drivers. NO OS told w10 -64bit?
• Bluetooth driver wrong. (missing or corrupted or not for your OS>)
• some of these KBD have addresses, the better ones for say office with 100 PCs, close and they would fail.
• so.... this must be reset if you get that wrong, RTM, the read the manual on your PC KBD.
• Bluetooth as a link storage place inside it, this allows fast reconnects ( A BT feature prime!) but can be reset an forced to relearn the KBD connection,  again RTM. (read how to reset this )
• I'd kick it to the curb and use  USB wired, no desktop ever needs wireless keyboards, ever, but gee...
• and last most BT have short range so if you are using 200inch TV on HDMI with you 25ft away on sofa with bluetooth failing ,DANG. really? I can't see you so,,, wow, what you have there I can never guess, at all.

NO OS stated, 8930 , what in the world is 8390?  I'm in USA and see no such thing here,

regressing BIOS is so evil I am silent,.

the driver must match your unstated OS.

no PC 8390 exists so can see what OS it came new with and if that is problem can I.

83xx came with w7 and upgrades to w10 are in fact problematic for any PC that old.  10 years old.

98xx is  0 to 3 years old, even brand spanking new, now. and does have BT/WIFE card inside,  and w10 loaded.

anytime BT fails go wired, and fix it when lazy and doing nothing much like stuck at home quarantined.

the manual on your PC shows wired keyboard not BT. so where did this BT keyboard come from?  maker and model, and is battery fresh.

if the battery does the BT side on the keyboard dies with it.

that is it, for sure if you typed, 83 by mistake. did  you?

Yeah, I had the exact same problem at the exact same time.  The provided solution, unplugging and then uninstalling the unknown USB device, worked for me.  Prior to that I could not scan for new hardware, but after following the directions I could do that and Bluetooth "came back".

That worked! Unplugging it is an essential step.

Thank you!!!!!!!!!!!  This worked.  My bluetooth disappeared AND my internet got VERY slow to non-working.  This has fixed BOTH problems.

My bluetooth just mysteriously disappeared on 5/12/2020.  I added nothing and downloaded nothing that i know of.  The provided solution, unplugging and then uninstalling the unknown USB device, worked for me.

That worked for me as well 

After hours searching for the resolution to bring back Bluetooth to my Dell XPS 8930, this solved it. The issue was created when I used the USB to charge my Bose headphones. This is an obvious bug that should, be addressed by Dell. Love the computer but would not have expected a simple USB charge to create a Bluetooth problem.