Weird video problem

[Conners]

Built my friend a computer a little over a year ago and recently it's been acting up. After booting it up the screen starts to shake and eventually turns all white with vertical lines. Tried my comp with his monitor and it worked fine. Tried his video card in my machine and it worked fine. Trying my card in his comp got the same results. My best guess is that its some kind of mobo issue, but I haven't run into anything like this before. I took everything out of his comp except video card and still got the same prob. Anyone run into this before? Thought I would ask before I shell out to replace the board.