check your plugs
if they're in, unplug them, re-do it.
Make sure your processor's in right and that the heatsinks plugged into the board. Make sure you plug the 4 pin connector from the heatsink to the board.
try unplugging any expansions, like your vid card or your HD and any IDE drives, then try to start it.
(If you're confident enough)
->Your best bet *(to troubleshoot)* would be to remove the mobo, place it on top of the anti static bag, on top of some type of carboard box. Attach your HD, CD rom drive, floppy if you have it, and plug your sound card and video card in.
Make sure you have the card, i'm assuming pci-express, plugged in snugly, and all the way, then make sure you have the power plug in. Make sure the sound cards connected right.
If all your connections are right, go ahead and plug in your power supply to an outlet.
You will need to "hotwire", so to speak, the board to check it. Find the pins labeled as Power SW. Stick a pen point between the two to establish a connection.
Also, don't forget the 4-connector from the PSU-> the board! That was my first mistake on my last build. (As well as the 24-connector).
If it doesn't start up after that, unplug one thing at a time to find your problem.
Another reason could be that your motherboard is corrupted, due to DOA (dead on arrival), or ESD (electrostatic discharge).
Lol, hope some of that helps you, that's what I did to get my rig working, and all I had was a DOA stick of ram, and I needed to update my bios. (because of a compatability issue)