Hi Just ran software update on my 2006 iMac 20", and there were three items (didn't check details as I usually do) and I assume they were iTunes, Snow Leopard security update and Airport Utility. Anyway, when the machine rebooted, the grey screen with an Apple and then a spinning wheel/sprocket came up but that's as far as it got, with the sprocket just spinning and spinning. Then I put in the Snow Leopard disk and tried booting from the DVD (cd?) holding down the C key after the hardware post BONG until the spinning wheel/sprocket appeared, but still the computer never got further than this and I while initially (with the C key depressed) I do hear a little more DVD action, that doesn't continue (which I would expect if the computer were trying to boot from the DVD). Any ideas about anything else I can try? I don't think we have the original grey Tiger discs that came with the iMac.