Well, it seems the plasma went bad.
Meaning, what happeneds in plasma (unlike lcd) is that if an image is projected for some time its burnt in the screen.E.g: the logo of a chanel (CNN 4 example) will be burnt forever if you wont pass the channel every once in a while or if your plasma doesnt have protection software(on her bios) meaning. The new plasma have several utilities for protection:
1. screen orbitier- a utility which will move all the pixels for 1 ms or so every once in a while (or it will blink the screen with white/black)
2. DPMS - will reset the screen power fuse.
note u can turn both OFF! , my guess is or the guys u bought it from didnt used such or their pixels got defected other way around.
Does it at least work with composite video? With R/G/B Cables? because normally drivers dun cause such problems......and it doesnt seem like its a controller problem...
from what i hear....Once a plasma go bad....it goes bad!
Don't worry too much, plasma also has a half-life of 3-5 years (meaning that it permanently loses half the brightness) so you only need wait 3 years and you'd need to buy a new one anyway. Plasma is a crappy technology at the moment; you get blurry pixels, quick burn-in, short half-life and it's expen$ive.