any beeps? can you see bios?
-reseat all devices especialy RAM and the VID card (if its not onboard)
-make sure that all power connectors are set on hte mobo, as well as if the vid card has needs for one as well
-go down to basics (mobo, cpu, psu, vid) see if bios loads up.. if yes, confirm settings correct then attach devices one by one untill you find it, then test that device on another rig to confirm its operation