Hmm.. It looks like a gradient with repeated coloured bands across it to me. At first I was going to say its probably the screen but when I think about it printscreen cannot be affected in any way by the display defects because it is a copy of video memory. This effect is not due to your monitor.
I'd be very suprised if it was due to your graphics card either - have a play around with the resolution and bit depth settings, but if that has no effect then it must be your card.
hth