Monitor Woes – please help!

For over a week now, the display on my monitor has been “flickering” – it either looks as if the monitor temporarily lost power, or else it resizes the windows a bit smaller and then returns to normal size, giving a bit of an “up and down” effect.
The support people have given me an APC, thinking it was a surge problem, have replaced the monitor, the monitor cable to the p.c. and have replaced the video card. Unfortunately these steps haven’t helped.

What else could be happening here? It’s really hard to analyze data and program when the display is moving around.