Its registration issue.
If you are still receiving : ERROR: Unable to start Bluetooth Stack Services?
Have you recently run a registry program for example Registry Booster 2?
If so then this may be the cause and suggest you restore to an earlier saved point from the RB backup.
I had the same issue and despite contacting Dell support and checking internet forums, the problem still occurred until I recognized it was the registry program new settings that was causing the start up problem.
I restored on the Registry problem to the back up and the issue has gone. I can even locate my BT TRAY.
Microsoft support don't seem to have an idea. Nothing new there.