screen resolution changes after reboot

Ok when I first looked at this pc the video. Didn't work at all I noticed a bad video card ( compositor we blown) well I got an nvida geforce 8600 gs and once I got the drivers installed and rebooted it was fine. Then I noticed it was running really slow and I ran malwarebytes and cleared some infections. Then installed avast and cleared a few more. Then rebooted and the video went to crap again I figured I lost video driver and I reinstalled them and it's getting crappy resolution. So I ran a program to clear off the drivers and reinstalled video driver and still all I get is 640x480. What could be the problem?

 

Greetings, gadg3t...

Need to know your OS version and service pack #, and a few other specs, such as amount of RAM, type of mobo, etc...

Does the machine have onboard graphics? If so, make sure your chipset drivers are up to speed, and try the onboard, see if the symptoms change...

You might also try disabling the onboard graphics in BIOS, and then reinstalling your nVidia drivers...

Keep us posted...