Display shrinking and "cracking"

I'm on my sisters laptop at the moment, but my computers display keeps shrinking and crackling (I don't think it's a videocard problem). What happens is, regardless of what I'm doing, the left and right side of my monitor will contract inwards, shrinking my display by like, 1-2 inches and sometimes has white lines (similar to what you'd see on a tv show not coming in too well) and will stay this way for a few seconds than jump back to normal.

Is my monitor pooping out (don't have a spare one to test it) or is my video card (almost brand new ATi 9800 Pro) pooping out?