A multitude of programs are locking up or unexpectedly quitting on my iMac G5. Wolfenstein Enemy Territory Unexpectedly quits, sometimes freezes system, forced restart. Age of Empires II Gold Unexpecedly quits 4-5 seconds into main menu loading, tried 1.0-1.05 and deleted prefs. (Does not happen on iBook) Unreal Tournament 2004 After updating to latest version, unexpectedly quits Myst V EOA Video freezes sound continues, forced restart "Mac OS X Unexpectedly quit" Football Manager 2006 Unexpectedly quits after importing a training schedule (this could be a bug in software) Rainbow 6 Athena Sword Unexpectedly quits every so often iTunes Unexpectedly quits every so often Safari Unexpectedly quits every so often (using tabs) Poser 6 Froze machine, had to restart 4 times before it started up again, unexpectedly quits now X-Plane Unexpectedly quits Apple Remote Desktop Unexpectedly quits every so often Marathon Infinity Unexpectedly quits while playing online (does not happen on iBook) After force restarting (holding down power button) the restart is usually much longer and sometimes does not complete. The fans come on full and sometimes it requires another forced restart (and in some cases like Poser 6, requires more forced restarts). I have deleted prefs of most these apps, the only game that has been successful for is Star Wars Battlefront (touchwood). I have repaired permissions frequently and that hasn't helped as well as defragmenting with Drive Genius 1.1.5, running Tech Tool Pro and Apple Hardware test has not yielded any answers. I tried two games on my iBook and the two do not show any of the problems the iMac does, I suspect more will also not have these problems. The RAM has been fine, it was put in new by a technician. I am running OS X 10.4.3 and are considering weather to reformat and reinstall the whole system.