I'm running a 5 month old 20" iMac with 1.5GB RAM, have had no troubles whatsoever until performing a routine software update last week to OSX 10.4.3 (from whatever was previous to that). When I restarted fan began to race and it took ten minutes to start up. Strange, but it ran okay after that. Yesterday it slowed to a crawl and wouldn't even pop open desktop folders. When I restarted (with all periphials removed) again fan raced but no start up -- just Apple logo on grey screen and spinning wheel. I ran the Tech Tools included on Apple Care disc which found no problems -- except it couldn't test Volume Structures (just learned that it might be an older version of TT which won't work w/ Volume Structure test), but now machine won't reboot past logo and spinning wheel, with the Apple Care disc unable to eject, and fan continues to race. Very frustrating, deadlines loom. Any help would be appreciated!