@ Basilisk Wrangler: Are you sure it wasn't something simple like needing a new battery or maybe a stick of RAM going bad? I can sympathize with you. My power supply died right after Christmas and I was worried sick it was something serious.
Well, it just doesn't boot. All I get is the gray Apple logo. I've put the boot disk in and I get a message saying "panic! We are hanging now..." and the system locks, not allowing me to do anything.
I tried reseting something by holding the power button while plugging it in. Tried booting with various keys being held (x, c, system s). Nothing happens, it just displays the Apple.
I assume you are at least getting the Apple start up sound--the boing?
Did you try holding down the option key while booting? This will locate all available bootable drives, including CDs. I assume you are able to get the original install CD or a bootable repair CD into the optical drive? (In other words, the computer will let you put a CD in?)
Seriously, try changing the battery first. It's a cheap, easy thing to try, and believe it or not, many things need that little charge to work right upon booting. Make sure you uplug everything, including the power cord, first. In fact sometimes unplugging the computer and taking out the battery for a half hour or so will reset everything and fix weird problems. If you press the cuda/pram reset button, make sure you only do it once, and briefly or you could cause more problems.
I really hate to say this, but if you are getting a kernel panic upon start up, which is what it sounds like from your description (is there a weird effect like a grey transparent window shade being draw down before the "panic" warning comes up?), it could be the logic board or something mounted on it--especially if it won't let you boot from the install disk.