Persistent Wake-from-sleep Error (!)

Question

I have thoroughly searched both google and these forums for help with this problem, and although it appears to be a common one, a solution has not yet been found :
Every so often and very randomly, my PB G4 12" will not properly / fully wake from sleep. When opening the lid, the computer makes all the normal noises as if it were waking, but the screen does not go on. Caps lock / Num lock keys behave as though the system were awake, and attached USB mouse is also lit up. All other aspects of the system are completely unresponsive - 'coma' (!!). The only way out of the lock-up is a force restart - i've had to do that at least 5 times this week.
I have tried EVERYTHING (i can think of!) to try to fix this problem :
reset NVRAM
reset PMU
reset PRAM etc, etc. etc!
trashed all caches etc..
reinstalled OS (twice!).
checked system with both TechTool Pro + Apple Hardware Test - both report that system is in perfect working order.
I've also tried trashing the PowerManagement prefs (some users have report some success in trying this).
No effect.
I didn't want to call tech support unless absolutely necessary, because i'm sure anyone who's called before has been 'helpfully' talked through repairing permissions etc...
Does anyone here have any ideas???!

Answer 1

Forgot to mention that this morning i checked logs after restarting and found this entry:
* First (successful) wake-from-sleep attempt: ****
Oct 18 07:44:29 PowerBook-G4-12-1GHz kernel[0]: System Sleep
Oct 18 07:44:29 PowerBook-G4-12-1GHz kernel[0]: System Wake
Oct 18 07:44:29 PowerBook-G4-12-1GHz kernel[0]: Wake event 0008
Oct 18 07:44:29 PowerBook-G4-12-1GHz kernel[0]: Sound assertion "0 != err" failed in "AppleLegacyAudio/AppleTexas2Audio/AppleTexas2Audio.cpp" at line 960 goto Exit
Oct 18 07:44:29 PowerBook-G4-12-1GHz kernel[0]: ADB present:8c
Oct 18 07:44:31 PowerBook-G4-12-1GHz mDNSResponder: Repeated transitions for interface lo0 (127.0.0.1); delaying packets by 5 seconds
Oct 18 07:44:38 PowerBook-G4-12-1GHz kernel[0]: [AppleUSBHCIController][StopIsochPipeRead] - mInt1IsochInPipe = 0 - numReadsPending = 0
* UNSUCCESSFUL wake-from sleep ***
Oct 18 07:50:05 PowerBook-G4-12-1GHz kernel[0]: System Sleep
Oct 18 07:50:05 PowerBook-G4-12-1GHz kernel[0]: System Wake
Oct 18 07:50:05 PowerBook-G4-12-1GHz kernel[0]: Wake event 0001
Oct 18 07:50:05 PowerBook-G4-12-1GHz kernel[0]: Sound assertion "0 != err" failed in "AppleLegacyAudio/AppleTexas2Audio/AppleTexas2Audio.cpp" at line 960 goto Exit
Oct 18 07:50:05 PowerBook-G4-12-1GHz kernel[0]: ADB present:8c
* FORCE REBOOT*
Oct 18 08:00:04 localhost kernel[0]: standard timeslicing quantum is 10000 us
Oct 18 08:00:04 localhost kernel[0]: vmpagebootstrap: 188791 free pages
Oct 18 08:00:04 localhost mDNSResponder-107 (Mar 20 2005 20: 31:47)[44]: starting
Oct 18 08:00:04 localhost kernel[0]: migtable_maxdispl = 70
Oct 18 08:00:04 localhost kernel[0]: 88 prelinked modules
Oct 18 08:00:04 localhost kernel[0]: Copyright (c) 1982, 1986, 1989, 1991, 1993
Oct 18 08:00:04 localhost kernel[0]: The Regents of the University of California. All rights reserved.
etc.
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