Ok.. So here it is.
I've used UBCD, Hiren's, and ERD. I've used multiple hard drives and even ran memory tests. Everything passes.
The computer will stay on while I use the above aforementioned cds and let me run tests all night long without powering down.
When I boot it from my windows xp cd to reload windows however it will go through loading the drivers and right as it goes to load up the screen to start the install it powers down instantly. I've also used multiple windows xp cds.
As a note.. I've also removed the batter and tried it like that, but it's always the same. I've fixed and repaired probably hundreds of computers and have yet to ever come across this problem. It really has me stumped. Any suggestions would be awesome.
The only other thing I can think of is that it is some kind of power problem and that piece of hardware causing the problem is only initiated when windows xp goes to load up but even ERD Commander is like a mini windows so I would assume it should have done the same on load, but it does not.