eMac with strange monitor resolution


I have an eMac running OS 9.2.2 and OS X 10.1.4
The user never uses OS X.
The screen resolution has been 800x600 since it was installed over a year ago, the user has never (to my knowledge) changed resolution.
The machine was turned on yesterday and the screen is now stretched (appears like letterbox on a tv) the right and left sides have partially disappeared of the screen and I have two black areas top and bottom.
I checked the Monitor Control Panel on OS 9 and the setting still said 800*600, I set the factory defaults but that made no difference. I can alter the size of the screen to fit the left and right sides back on the screen but they appeared very squashed.
I thought at first that this was probably an OS problem, so I tried starting the machine with OS X and that has exactly the same problem.
Now unfortunately I am not a MAC expert, I work primarily with PC's (Windows and Linux).
Can anybody tell me whether this is a hardware (CRT) fault or OS/Firmware related.

Many Thanks
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If you're unable to make any changes to the display to have it fill the screen vertically, then the machine either has a problem with the display itself, or with the graphics controller; given the nature of the problem (black bands at top and bottom) I would venture the problem is more likely a hardware problem wit hthe display (CRT tube) itself than the graphics chip.

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You could try zapping the pram or nv ram.  if that doesnt help, reset the pmu.
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