graphics card problem or mobo?

I had a 7800GT but it started giving me artifacts and lines everywhere. I bought a 7600gt to see if it was the cards problem. In the beginning the card was working fine until after 30min. My monitor wouldnt read the graphics card un less i pushed down in the front right side of the card. So everytime I start up my comp, i hold it down than turn it on. Sometimes it will take several attempts of pushing the graphics card down for it to work. When I play any games sometimes artifacts start popping out randomly and than if i push down on that card again it will go normal. Now my windows boots with red green colorful lines everywhere. Still requires me to push down for screen to show up but now theres lines everywhere. I took the graphics card to a friends house and it came up with the same problem, but I didnt have to push down on the graphics card on his comp. should i buy a new graphics card and see if it still works, or do i need to get a new mobo too?

My comp parts:
Asus A8N-E Mobo
antec 500watt
evga geforce 7600gt
amd ahtlon 3700+
2gb ocz ram

If you have to push down the vidcard for it to work, there probably is an issue with the PCIe slot. Dust off the inside of the slot, clean it up as well as you can and try again.

That issue could also be confounded with a overheating vidcard issue. Grab Rivatuner and increase the fans to 100% and give it a try.

Thanks for the help. But when I used my video card on another computer the same problem occurred. I guess I screwed it up real bad by pushing it down and it's finally caught on. I'm wondering if i should attempt to buy another graphics card, or if I need a new motherboard and graphics card now? Because this happened to the 7800gt and 7600gt, where both are now bad and required pushing on for the screen to show up.