Check to make sure nothing has worked lose on the mobo - RAM, sound & video cards power, IDE & SATA cables. If all OK, remove all items except power and one stick of RAM and see what happens. If still nothing, try with another stick of RAM. If still nothing suspect blown motherboard (some, I think have a replaceable fuse, but others wil have to advise on this). If POST suceeds, add one unit at a time until POST fails to identify damaged unit.