Try with one stick of memory only in different slots and if dont work try same thing with a different one. unplug everything else and see if it post. If you have put an add-on video card remove it and use the onboard one. mobo, cpu, one stick of memory and remove all usb stuff, hdd, optical drives etc.
see if it post.
if not still posting then remove the memory stick..it should beep at startup because the system lack the memory..if the system does not beep then your mobo is dead. but be sure to look if theres an onboard speaker on your mobo or one on the case correctly connected to the mobo.
http://forums.redflagdeals.com/archive/index.php/t-874235.html
Follow this link also the guy seems to have the same problem as you.