Dust out your computer really well, unplug every peripheral, including power cord, USB's, and Ethernet.... hold power button down for about 30-45 seconds to do a hard reset (will help reset CMOS) and try to reboot, plugging in each thing 1 by 1, power last.
If that doesn't work, try to pop out CMOS and put back in, same with RAM 1 by 1.