Hmm picking up a mobo on ebay.... not the best idea. Without proper handling static can short the board out before it even gets to you. I have fried a mobo making a dumb mistake like that. I have used 3 DFI boards so far and I've never had a problem with the board itself it was always a user error problem. If you are concerned it is the board you can test it.
Remove absolutely everything. Then with only the PSU connected to the board, hit the power on button on the board and see if it turns on. Now it will beep or display a diagnostic LED code because nothing is in the board, but if it turns on then it is a power switch problem (unlikely).
My guess is the board is dead. Those mob's are damn sensitive, which is why most ppl wear an anti static wrist band while building, or keep themselves grounded somehow.