When booting up the GA uses basic settings, however, when the OS takes hold IT'S using enhanced mode drivers. Try booting in Safe mode for a check.
The drivers may be corrupt and may need to be re-installed. This also may be symptoms of a bad connection at the monitor cable/GA port.
Thanks, mechbas, for your reply!
Which drivers do you refer to? I think I'd have to re-install drivers from a mfr's. website, as emachine supplies only a "Restore" CD.
Re: the monitor cable/GA port: what does "GA" mean? (Wikipedia didn't say.) I do know that the monitor cable has had an apparent break for many years, so to avoid having my screen go shocking pink, I kink over the monitor cable against itself: then the color's OK.
New development: I just changed, in Control Panel, the monitor's refresh rate from 75 Hz where it's been ever since I got it (about 11 years) down to 60 Hz, and, voila!, the screen vibration stopped. It did not stop tho at 72 or 70 Hz. And I'm not seeing flicker at 60 Hz, which was why I wanted a high refresh rate.
Now that it ain't broke, I don't wanna "fix" it. But I do want to follow up with the drivers idea of yours.