have u replaced the CPU?
as once I didn on AMD (replaced it and used a new thermal pad (forgot to peel off plastic from it) and my workng AMD refused to start (oh my God! what had happaned, i though, as on same board my other AMD was working, and this not), I wasted my money I thought, but once I turned my FAN, nothing happened to the thermal pad 9as it was supose to have changed shape as I applied CPU die pressure, on close look, i realised, it has still plastic on, and AMD Barton was failing to start just because of that plastic. thinks there isnt heat sink over it. (impressive)
does ur CPU fan runs?