List All components. (Specifics on Power supply Needed, unless already done)
List the cooling setup and heatsink.
When did this problem start?
Did you add any new software or hardware as of Late?
Dissconnect all components except CPU, Video card and One Stick of RAM. Clear the CMOS by removing the small coin like battery for Two Minutes. Remove the motherboard from the case and place it on a hard non-conductive surface.
Turn it on and if it POSTs, Shut down, put it back in the case, add one component and repeat the process until it no longer boots. The Component that was added last most likely caused the Non-POST and should be RMAed and or Replaced.
Report Back.
(lol)