I've been having some video card issues ever since I've got my computer about 7-8 months ago, I've had to replace the card once already, after only 3 months. And now this one's been having the same issues. Both where diffrent companies (first was EVGA, second was BFG) Geforce 7900 GTOC's. Only similiarity is that they're both factory overclocked.
What happens is, it will start of with "dots" on the screen, and they'll show up randomly and it gets worse overtime, texture's in 3d games will start to stretch and flicker aswell, which also get's worse overtime, to the point where any 3d games are unplayable. I've tried diffrent driver's and all that with both cards, and the temp never excedes 65c or so while playing game's for awhile. The card has lot's of room to breath, and i clean the computer pretty often. One thing i forgot to mention, is that the second card lasted a bit longer, and isn't as over clocked as the first one. And also, when the first card started acting funky, i opened the side and put a fan up to it, which kept it around 45c while playing, but it still did it.
I dont really want to take it down to the tech shop i got from again, because i later found out they are not to be trusted. (And when they replaced the first card, they didnt know what was happening anyways) I've came across a few things saying that these factory overclocked card's have a short life span, can anyone confirm this? or could it possibly be something else? (Also, when i picked up the computer after getting the first card replaced i noticed that they use megnetic screwdrivers if that matters). But i havnt had any other issues with the computer aside from that, so I'm hoping it's just the cards.
Have you tried to underclock the card using something like Riva tuner or Coolbits? , if the artifacting is not reduced when the core or memory are lowered then either your card is shot or it may not be getting enough power, is your PSU up to the job? read this if you are unsure :- http://forumz.tomshardware.com/hardware/PSU-101-102-ftopict198276.html , as for factory OC'd cards being short lived, my XFX 7900GT OC has been fine for the last eleven months or so. HTH
I tried underclocking it like you suggested (tried a few settings), and it didn't make a difference. But as for the power supply, combined +12v is 42A/504W and the video card requires 20A+/320w. Which should be enough right?