Lynn’s Monitor Problems
Dear [Lynn],
I don’t like the flat panel screens yet. They’re getting pretty good, but their resolution, brightness, and over all clarity, in my opinion, still does not match that found in those good old CRTs. So hold on to your CRT for as long as you can.
Now, to the problem at hand: It sounds like the picture tube might have become magnetized. Most monitors automatically degauss (demagnetize) themselves when you power them on using the power switch on the monitor itself (Not the computer power switch). Try turning the monitor itself off, letting it sit for a half-hour, and then powering it on again. Most make a brief humming sound for a second or two when you turn them on after this. This sound is the demagnetizing circuitry working. If you don’t hear it, this may have become defective in your monitor and will require repair or replacement.
It might also be that the monitor was bumped  hard.  A thud can goof up the purity adjustments located on the neck of the picture tube inside the back cover, and create symptoms such as you describe. To correct this, you’d need to take the monitor to a TV or computer repair shop and have them readjust it for you. But, if the bump was  very hard,  it might have bent the shadow mask, which is a fine screen of metal just behind the glass surface in the picture tube. In that case, all the purity adjusting in the world won’t fix it, and your only option is to replace the monitor.
Also, monitors do as you describe when there’s a strong magnetic field nearby, such as is found around motors, transformers, heaters, and other high-current appliances. Speakers and subwoofers not adequately shielded can also distort your monitor’s colors. Try moving such devices away from the CRT and see if the screaming green goes back to normal.
Tom