try to hear what the asus speech reporter is saying (plug in your headphones/speakers into the green plug on the onboard sndcard)
, if its not saying anything then i dont know, usually asus mobo's speech reporter tells u whats wrong why it wont boot up.
EDIT: if it doesnt say anything then its probably a broken mobo,
Check if the clearcmos jumper = ok, happened to me once a mobo didnt boot up cos there wasnt any jumper there...
Hope this helps