I've got a late-2007 2.0GHz iMac w/1GB RAM, 750GB Western Digital HD (replaced 2 years ago after an HD failure) running Snow Leopard. I woke up this morning and found it frozen on the screensaver, so I did a force reboot and it sat on the grey Apple logo for about 5 min. Did another force reboot and only got a blank grey screen with an internal clicking noise that repeats every second (kind of sounds like a clock, but goes DA-DUNK, DA-DUNK). I tried booting from the Snow Leopard disc and the mouse cursor came up, but neither the HD nor the disc appear in the selection. I tried resetting the PRAM and SMC, but no luck. Tried D, Command R, S, and T, but got nothing. My first inkling was that it's a hard drive failure, but I hadn't experienced any of the usual signs prior to this. It had been running a little slow for a while and felt really hot to the touch, but that was probably due to low RAM and heavy use. Also, I was able to boot from a CD just fine when I last had a hard drive failure. Could this be a dead logic board? It's probably time for a new machine anyway. Luckily everything's backed up to a Time Machine drive. Would the cost of taking this thing to the Genius Bar and having it sent off for repair outweigh it's actual value?