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that's easy, something is touching a hot wire to ground, hard thing though is finding where. I would take the front panel off and look at all of the points where the aluminum goes into the case. Look for stray wires, wires that may have had the insulation stripped off, and possible loose screws that either aren't all the way in or actually out all together. Good luck and let us know what if anything you find.
 
Something might be touching the fan in the front preventing it from moving. Had a similar thing happen to me on a newer model. Nothing a little thick insulated electrical tape couldn't fix!
 
The user replied on youtube:

Hey man, thanks for all your help. Got the case issue figured out. There was an obscure little wire that was being pinched at the bottom of the computer, down by the cooling fan, which, when the case went in all the way, was causing it to ground out. Touchy!
 
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