thanks a lot! any advice is appreciated!

After all that waffle and piffle, you never even once conidered removing the
****ing DVD drive. Right?

Wow, you're quick to jump to conclusions. If you read the post, you'll
notice that:

"...I've tried replacing the power supply, and I've tried removing all
my hardware (other than
RAM), so I'm thinking it must be motherboard related."

So yes, of course I removed the DVD drive. Logically, the first thing
to try...