|OK, I recommend this...|
First, take the motherboard out of the case. Remove the power supply, one memory stick, video card and processor, from the case as well.
(Now... make sure you are standing on an antistatic surface)
Lay the motherboard out on a flat surface on an anti-static surface (preferably wood and/or antistatic sheet).
Next, add the memory stick, video card (if not onboard) and processor. Make sure they are all seated properly.
Next plug in the power supply and attached the connectors to the motherboard. Then, find the two pins that the case power leads (ATX-PW etc) connect to. Now, touch a small flat screwdriver over both of these pins briefly (don't touch anything else). The board should power up and you should see if it posts, on your monitor.
Using that method, if it doesn't post, your motherboard is most likely bad.