First of all, I have installed Lion, so there is no installation disk to try and boot from, I can't get my 24" 2008 imac to load past the grey screen. I've unhooked all the cables, held down the power button for 5 seconds, reattached the cables, powered it back up,while holding down the P-R-command-option keys, no luck. I've tried starting it holding down command, command option, shift, no luck. I did get an arrow once, I think I was holding the option key down when I started it and got an arrow. I've unplugged it several times, all the cables, hoping it would reset, but it hasn't. Can someone help me. I'm hours away from a Genius, I'm on my own here. I hear the tone when I boot, but I can't get to the Apple logo. My time machine is backed up to an external drive, thank goodness, I can hear the motor whirring when I first boot, it just won't finish the load.