Interesting.
Try when booting up hitting F8 just after you hear the post Beep.
I would say not being able to go into safe mode may be an indicator of other OS issues, but I still believe for the original issue of redetection, that removing what we call "ghost drivers" in device manager (in safe mode) may be the solution.
Some of the older HP Pavillion's have up to 18 monitors listed when you go in there in safe mode, however you won't see them in normal mode.