Can't boot from any disk!

My computer has been having kernel panics like crazy. I've managed to get the info off the hard drive bit-by-bit by leaving it unplugged overnight then trying in the morning. However, I now can't get the computer to rebbot on start up to run disk repair. My Snow leopard disk is inside (I can't get it out), I have a rebotable copy of another mac on a usb external, but can't open to re-boot on either pressing option or C on start-up, any other ideas??