Trouble getting my video card to work full

I bought a new powersupply this week so my Nvidia 7900 GTX card would work. Now when i put it in and turned my computer on I get little pixels in random spots on the screen. Which never happened when I ran the on board video. Now today when I load vista I got a blue screen. I am pretty sure its because of the video card I added cause everything works fine when I take it out. I downloaded the lastest drivers too. Any solutions? I thought it couldve been the video cable till I got the blue screen. I hate to get a new card as it was about 500bucks when I got in 5 years ago.