Imac help

I have an IMAC running 10.5 After my dog knocked out the plug, I'm getting a gray screen with flashing question mark. I've gone through the forum and tried restarting and holding the Option key. Nothing. I've restarted holding command/option/p/r. Nothing. I inserted my original startup disk, Mac os x install dvd and restarted holding the C key. The issue remains. Still have a flashing folding with a question mark. Does anyone have any other suggestions?
Thank you

The gray screen with a flashing question mark usually means that the system can not find a boot drive. You said you tried to boot with your original Leopard DVD and that didn't work. If you are sure the DVD you tried booting with is the original install recovery DVD that came with your iMac, it's possible the optical drive is not working right. Did the iMac have any problem playing CDs or DVDs?

Yes, it's the original dvd and yes the drive did play cds without a problem. When I restart holding the C key, the computer hums and then the dvd pops back out.

As a suggestion get a cheap external optical drive and see if you can boot from the Leopard DVD on that. iMacs have slot loading optical drives which have a high failure rate at best. Who knows what doggie could havce damaged.

It does sound like the drive is not working right if it's ejecting the Leopard DVD. If the DVD is not defective or scratched, you might try blowing some compressed air in the drive. Sometimes the lens can be dirty and that will cause the disk to be ejected. The drive laser needs more power to read a DVD especially since the Leopard DVD is a dual layer bootable disk. It may read and play a CD or even a single layer DVD OK but not a bootable double layer one.