That sounds like the card is actually defective. Do you have another to try because it also could be the board at this point. Actually remembering all the "ill" you said about this computer, there is another possibility and that is ram is no good in spite of new ram change you did.
I would download and run memtest86...now that takes a while because you have to do 4 complete tests and each test has 8 passes and as much as one error you have your culprit. I wondered about them sending you replacement ram in the mail. Ram these days is so tough I never buy anything unless the configurators at Corsair, Kingston or Crucial list that model number for that board. Oh and can bad ram show up a year later even, you betcha! Ram errors are real nasty. They can be different on every boot and appear like software problems when the ram is close but not matched. I had a problem one time where bad ram in a desktop shut down a nearby laptop's computer access to Vpn. I had to go to a friend to ask a dept head at RIT if that was possible, even though I knew it was happening as I pulled the ram and the network opened up and he responded yes it could happen. I thought I was in the "Twilight Zone".
www.memtest86.com
You can try the Vista memory test but it is real elementary and may show nothing:
Run, "mdsched.exe" and hit enter. So if it shows something, great if not I would still run memtest anyway to be certain. But is sounds like bad video card or bad video slot. Is this an Ecs, Pc Chips, As Rock or Fic motherboard incidentally?