Did you mount the motherboard to the case using the brass stand-offs or did you mount it directly to the case? If you did use the stand-offs did you make sure they all lined up with the holes on the motherboard.
The stand-off's must be used and if any of them are out of place the PC will not power up.
Here's a picture of a stand-off
And they attach to the case like this
The stand-off's must be used and if any of them are out of place the PC will not power up.
Here's a picture of a stand-off
And they attach to the case like this