Got a blank screen (g4 /os 9.2.2) at start up. . . .
Do you have OS X on the machine, as well? If so, what happens if you boot from it?
Does blank mean the screen stays black but not when you boot from a CD, or do you get a blinking question mark? Do the fans work?
If the machine is not loaded with OS X, as well, but you have or can beg, borrow or "liberate" a System X DVD, you could run the DVD's Disk Utility SMART check to see whether the drive is dead or dying. (I think all G4s came with SMART drives and enough RAM to run OS X.) But I'm not sure which versions of OS X include the SMART check. Maybe all of them do.