Q: Installed 10.4.11, stuck at Apple Logo screen, cannot re-install OS X.

Ok, so my MacBook Pro is currently in the shop having the motherboard replaced because of some weird screen issue, so I booted up the ol' iMac to use in the meantime.

It had the original OS installed and ready to sell, so it booted in 10.4.6. I thought I'd at least update it to 10.4.11 while I was using it.

I forgot that the last time I tried it was stuck at the Apple Logo screen with the "clock." I wasn't too panicked, so I put in the install disk and hoped to just reinstall 10.4.6 and get rid of the problem.

I can't get it to boot from the disk. I have tried holding C, Option, Command Option Shift Delete... nothing works. I hear the disk spin and then it goes straight back to the "clock" and sits there forever.

I even tried using my MacBook Leopard disk and that did not work either.

So now my computer is useless. It is stuck at the load screen and I cannot seem to even reload the operating system.

Can anyone help? Thanks in advance.