This is about my dear old iMac, late 2006. Some six weeks ago I replaced the hard drive (you can read about that here: http://forums.macrumors.com/showthread.php?p=20855101#post20855101) and all was really well. Performed like a charm. Then, yesterday, it wouldn't wake up from sleep. I rebooted and after a normal start-up, it hangs at a grey screen. I found Apple's instruction manual on what to do in case of a grey screen, tried all (peripherals, cables, pram and the other abbreviation thingy, checked RAM, etc.) but to no avail. It will only boot in Safe Mode now. Anything else I throw at it, and it won't start up, like: - original Tiger install cd: starts up, then hangs on blue screen - an external (and healthy) Hard Drive, connected with a sata to usb adapter: hangs at Apple logo with spinning ball. Much to my surprise I was able to do a Hardware Test (so cmnd+D worked), but all was well. When in Safe Mode, Disk Utility says the hard drive is all right. So, I'm thinking, this is not Hard Drive related at all. Any suggestions? Is it kaput? Beyond repair?