Windows Error Visual Adaptor?

Does anyone have any suggestions here is my story: A week ago my computer displayed a message that said windows was unable to start. To make a long story short I did what the system suggested by running my repair cd. When that didn't work I contacted microsoft who couldn't figure the problem either. They ended up walking me through reinstalling vista and later upgrading the computer to windows 7. It was really strange because the computer loaded the programs but the screen would have these blue lines on it and the windows error failure to start message kept appearing. As a last ditch effort I took my computer to a repair shop. They diagnosed and said my memory was fine and my motherboard was too. They problem was with my visual Display adaptor. For 120.00 the replaced it. End of story right? Nope wrong. I get the computer back home reinstall windows 7 everything was fine until I started getting the blue screen the first time it happened I ignored and figured it was some kind of one time fluke. Then it happened again. The message pretty much says. That windows detected a problem and shut down to protect my computer. To run a system diagnostic utility, and a memory check. Remove andy newly installed hardware or software. Now whats even stranger is that when I hit the power button and my computer comes back to life it loads the same screen I was on before the blue screen as if nothing happened. I went back to computer shop and they seemed to think I may have installed windows 7 wrong for 150.00 the would do it for me refreshing the system first. Its not that hard to upgrade a computer but as they said they are the pros let them give it a try I figured fine go ahead. Yesterday I picked up the computer everything was fine. Well you guessed now Im getting the blue screen again this time it says the same thing only this time it says try changing video adapters. .....Ive already dont that. Is there a possibility this one isn't compatible with my dell computer? Ive checked my memory myself, and ran a system diag. No problems there. Im at a loss. By the way the video adaptor that they put in seems to be working fine. No blue lines at all.