Toshiba M645 Shutsdown Randomly

[voidgere]

The details:

-When it shuts down, it takes a random amount of time (3 seconds to a full day) for it to regain the ability to turn on.
-It does not shutdown during Windows 7 installation (left on for 3 days at the "Partitioning" stage).

What has been done up to this point:

-Dismantled entire laptop and cleaned every spec of dust found.
-Reseated CPU and RAM.
-Redressed CPU thermal paste with new.
-Checked power pack and battery in another laptop (I work in a PC shop).
-Flashed BIOS to the most current for the model.

I am really just looking to see if anyone has any additional thoughts that I may have overlooked. An extra set of "eyes" is always a good thing to have on something like this.

 

[voidgere]

Just updating this thread:

I tore the laptop down again looking for scorch or bad capacitors and didn't find any. I guess if this thread goes cold again I will close it and declare the cause lost. I got the laptop for free so I am not out any money. I just would hate to shuck out 250 dollars for a new motherboard (about the best price I could find) and it still not work.

Thanks everyone for all the views.