Dots, lines, bad images - graphic card or...?

A whole lot of symptoms:

1. dead pixels,

2. distorted images, slowing images, letters going down or up, instead of straight. All corrected as soon as another action performed (for ex. in WOrd the letters went own after typing letter"p", but went up as soon as i opened Finder, or did something else.)

3. does not wake up from sleep, black screen, light not blinking - dark

4. will have moments when the screen goes gray and asks to restart the computer 5 or 6 times in a row.

I have iMac Intel.

It all started when Windows on parallel virtual machine crashed.

The monitor, display suffered.: besides dead pixels here and there and everywhere. there where distorted images, frozen movements of windows coming up and down. After a second crash, had to reistlall OS X

For example: a safari icon on the dock, could suddenly become just a set of lines.

Can a graphic cad suffer because of a computer crash, or maybe because of the need to turn the computer off by button versus menu?

Maybe power shortage cause problem with graphic card. But how come installing parallel desktops makes distorted images appear more and more each time.It cant be software incompatibility though

Here was what I tried so far:

1.reinstalled Snow leopard

2. checked hard drive with a software and it says that Hard drive is fine

I think it is graphic card, but I know very little. Please help me figure out what is it.