Help with Asus P3B-F

My P3B-F is dead after two years of very light use, not overclocked. It beeps continuosly with alternating high note and low note, no post on the screen. I don't see any swollen capacitors. I've tried replacing every component(cpu, memory, video card). The place I bought it from says it has a 3 year warranty from Asus - is this true? I tried to register it in the Asus site but it tells me that my serial number, which I got off the motherboard, is invalid. Any suggestions would be appreciated.