Hangs or Kernel panic on boot -- won't boot off DVD or hard drive

Question

I have a MacBook running OS X 10.5, and when I tried to turn it on today it froze at the gray screen with the apple logo. No spinning progress wheel appeared.
In an attempt to fix this, I unplugged my external hard drive and my ethernet cable, leaving only the power cord attached. Attempting to boot from the install DVD results in a kernel panic. It won't boot in safe mode or single-user mode. In verbose and/or single-user mode the text displayed for the boot sequence appears normal until the following block of text that comes right after "The Regents of the University of California. All rights reserved.":
MAC Framework successfully initialized
using 5242 buffer headers and 4096 cluster IO buffer headers
devfsmakenode: not ready for devices!
IOAPIC: Version 0x20 Vectors 64:87
ACPA: System State [S0 S3 S4 S5] (S3)
This is the last block of text displayed; the system hangs at this point. I've also tried resetting the PRAM (no effect), and on the offhand chance that this could be caused by a loose RAM module I ejected them both from their slots and reinstalled them, so I know they are seated with good connections.
Any suggestions or help would be much appreciated!
Thanks,
Steve

Answer 1

It has 1 GB of RAM, so I tried booting up with only one module. Neither one of them solved the problem, although oddly enough in Verbose mode this time instead of stopping on the error the I mentioned before, it continued a bit further and gave a kernel panic. This was the same for each module.
I'm coming to the conclusion that at this point it's probably either the logic board or the CPU, and will probably be expensive to fix -- the warranty ran out in August. I suppose that it's possible both RAM modules are bad, but it seems very unlikely that both of them would be.
I suppose I'll just have to bring it in for servicing and have it checked out.
Thank you for the suggestions.