the long sleep

[pantosj]

Lately my iMac G4 is having problems when put to sleep. The screen goes black as usual but sometimes the computer doesn't actually sleep...you can still hear it whirring inside and my external firewire hard drive light remains on. When I try to rouse the iMac, the keyboard and mouse are dead. I've tried unplugging and replugging the usb for the keyboard. Tried swapping usb ports...all of that, without being able to get the keyboard or mouse to work so that I can re-activate the computer (or at least get the screen to light up again).

Any ideas?
-Ryan