try restarting your computer...i'm not really understanding your problem.
Maybe something is loose inside your case. If you modded your pc (and even if you didn't) and you have knowledge, i would open up your comp and make sure everything is seated properly...Ram, Gcard, everything. Also try clearing Cmos...were you overclocking by any chance? Sometimes clearing Cmos fixes these kinds of probs...
don't reformat, this doesn't sound like a software issue...something probably hardware related died ...
the screen going black sounds troublesome ...if all else fails pull out your Gcard and try installing on-board graphics. your card may have gone bad.
haha or it could be your mobo ...so many things to go wrong.
if ALL ELSE FAIL rebuild your computer...disconnect everything and start building with bare essentials and try booting in safe mode.
