WetGeek This is amazing. I happened to have a Budgie live USB handy, so I booted to that. And Bluetooth worked fine.
Huh! What that says to me is that either: (a) the Solus installation on your M4800 is corrupted, or (b) an updated file since the ISO release used for the Live USB screwed things up, but royal. My guess is on (a), so a Solus reinstall would resolve the issue. If you feel like fooling with it, boot into the Live USB, install Budgie from the Live USB and see what happens. I'm slapping my head that we didn't think about a corrupted installation sooner.
WetGeek Given the black screen on the M4800, there's no telling what else might go wrong with it.
Yup, my theory about a corrupted installation aside, the motherboard might be giving up the ghost.
WetGeek I'm still looking forward to the newer Latitude, so I'm not going to cancel that order.
The M4800 has to be 7-8 years old now (2014?), and once you move to the newer Latitude, you won't want to go back. If a corrupted Solus installation turns out to have been the problem, you can repurpose the M4800 as a test machine or put it to other good use.
BTW, when you get the Latitude, it would be a good idea to update any firmware that needs updating, in addition to the BIOS.