twice today my pc screen has gone black for no apparent reason... once while playing skyrim and once while web browsing... my rig is a gtx 560 ti, 4 gigs of ddr3 ram, 1680x1050 monitor, amd fx 6300 psu and crappy 500 watt psu that came with my case... I suspect it is ethier my monitor or gpu... my monitor is an older one my dad used to use... the gu is a "refurb" off ebay... everything else is new... what could it be??? is it my gpu??? please help, and thank you!!!