I am running Snowleopard on a 24" white imac bought in 2007. My system has been somewhat temperamental for a few weeks, crashing out on me when waking up and generating random artifacts onscreen during use. I noticed also that the hardrive recently renamed itself as "EMI Boot" when booting using the option key (although it worked fine). Now, when booting, the apple logo appears, followed by the spinning wheel and a blank gray screen. Then nothing. The same thing happens when I try to boot using a mirrored backup drive or a separate bootable drive with a different version of OSX. The imac drive will, however, launch using a MBP in terminal mode without problem. I have run Diskwarrior and fsck on the drive. No difference. I've tested the RAM using memtest in single user mode. RAM seems OK. I dont have the original installation disks, so cannot run the diagnostics. I'm coming to the conclusion that this may be a logic board problem but would appreciate any suggestions.