Screen going black

It all started when I was playing wow and my screen froze with a bunch of blue lines on my screen, so i restarted my comp and I saw a bunch of A symbols and my screen went black before the log in screen even showed up. So I decided to try my old 6600gt video card and it worked fine for about 4 hours until i opened up a new game and my screen just went black so i tried restarting but this time I got no A symbols or anything my monitor just flickered and was black. I don't think its my video card anymore since this happened on both my 7600gt and my 6600gt so i'm wondering what else could be causing this.

ecs motherboard latest bios
intel e8400 cpu
4gig patriot mem
xfx geforce 7600gt
420w power supply

Had to remove my old 6600gt that i was useing and started useing the onboard video on the motherboard just to get a display. But when it boots up i noticed i dont see any post information. Power button on monitor blinks green then windows log in pops up and i can log in and it works fine. Tried clearing cmos several times to try and get post information to display with no success. When i install the video card fan runs on card but no display ever comes on unlike when useing the onboard atleast i get the windows log in screen and can use my pc. Im going to try and delete my nvidia driver and reinstall my card with the latest driver 182.50 that just came out 4/2/09 and see if that works.

Power Supply crapping out??

I have a 420W power supply thats really old, im not sure about any other info on it. Im going to try and upgrade my power supply and if thats not the problem then I was thinking maybe the motherboard but im not sure.

Its a turbolinx 420w, my volt meter says its at 12.23v and the 5v was 5.23v