OMG I bet I'm seeing a dozen guys a week with this problem now! Why the sudden increase, I have no idea!
The answer is obvious if you took time to read the first post in this forum, a circuit on the back of your motherboard is being grounded by a misplaced mounting post.
You see, when you first plug in most computers, the fan will spin for 1 second (roughly). Then the only way to power it on is to use the power button. I assume you have the power button connected to the power button plug on the board, right? And if nothing happens after that, 90% of the time it's because your board is grounded.
Now, that leaves a 10% chance of me being wrong. If I were a gambling man, such odds would be oh so sweet!
<font color=blue>Watts mean squat if you don't have quality!</font color=blue>