OK sounds disturbing.. You have the same unit I've been happy with for some time.
So....You either have a Hardware of Software issue- First check the Hardware:
If you have it...use the CD
Apple Hardware Test. that came with the computer
Once you get it in the CD drive - power
off the computer.
Then,
restart it while holding the "C" key down. This will makethe computer boot up from the CD and from there you can run theon-screen menu diagnostics...this will give you a detailed report ofeverything hardware wise good or bad in your box.
If all hardware is good then you will probably have a software issue and, you may need to Restore the Mac..with the
Software Restore disks ( 4 CDs) that came with your model, then reinstall OSX ( 2CD) (depending on which OS you are using)
Here's a quick link to Apple's info on doing this.
Apple I suggest giving Apple a call even though the G4 is probably out of warrenty. Apple has provided me with out-of-warrenty phone help(usually late at night when they're not busy) for free and gave megreat help.
Also... check in your area for any Mac User Groups..(that's right- MUGs). any missing diskscan probably be easily located there, and these folks love to help.
Good luck...danielj