did you take the board out of the case and see if it worked?

I had a board once that I sent back 3 times, and the the third time it still didn't work. I took the board out of the case powered it on and it worked. There was a screw that was causing a short in the motherboard. That was all.

Just try that then if it doesn't work call tigerdirect up tell them its your last time ordering from them, (I hate tigerdirect) and order from http://www.tcwo.com or http://www.pcprogress.com

Good luck.