yo i bought the same mobo and had same problem look at my earlier post "issue with m/b?"
return it and get another.
atm im in the process of getting another new one
asus mobo's get defectived very often, well not often but relatively high compared to others... these mobos get purchased like hotcake so the chnace of getting a defective one is high
also check out this link and see if this is similar