Graphics dvi, hrmmss. crashes my pc ?

Why does DVI make my computer crash, and scramble the screen on another computer?

I had a loose connector on one computer, and the screen went flashing on and off and made my computer lock up after a while.

I changed the videocard in that computer to see if the same thing happened, and I changed it for a 9800xt. It made my screen look scrambled and as if I clocked it too high...

Another computer of mine crashed while I connected and disconnected the dvi cable as well.

What's up with that?