Can you try it on another machine - even laptop?
Got a spare video card of any sort: at 640-480 a dead cockroach with a flashlight battery'd almost work.
ie - the card is suspect until it isn't, and for the problem to be on one half - sounds much more like the card losing some VRAM or what decodes to that, than what the e- stuff in the monitor might do.
Luck,
Ashton