iMac shuts down on boot - Please help

Help, I have a possible dead imac, it was running OSX10.5, infact I had only done a clean install a couple of weeks back, and was running great since.
I hadn't used it in a few days and decided to boot it up to get some work done on it today, but during the boot I hear the fans/drive spin up then it shuts down

I have tried the apple+s boot, and ran the File System Check, but it shows the following;

** /dev/rdisk0s3
** Root file system
** Checking journaled HFS Plus Volume.
disk0s3: I/O error.
Invalid B-tree node size
(3,0)
** Volume check failed.
/dev/rdisk0s3 (hfs) EXITED WITH SIGNAL 8
-sh-3.2#


I hope some one is able to desifer the above, and can guide me.
It looks to me to be a boot disk error, but I am not that familiar with Mac boot systems.

If it helps, I have a Mac Book, that is also running OSX10.5, can I use this to boot the iMac??

Pop in the Leopard install DVD and try to boot from that. If any joy go to Utilities and run Repair Disk. Otherwise see if you can get hold of a copy of DiskWarrior 4.1, the best drive utility fo Macs.

harryb2448 said:

Pop in the Leopard install DVD and try to boot from that. If any joy go to Utilities and run Repair Disk. Otherwise see if you can get hold of a copy of DiskWarrior 4.1, the best drive utility fo Macs.

Click to expand...

I tried putting the disk in, it doesnt even get as far as reading the disk, and I can't get it to boot to get into Utils or to run a repair.
I am away to go hunt for DiskWarrior as you sugested tho, cheers.