Take everything out including hard drive, RAM, graphics card, etc. Leave only the CPU installed. Disconnect the keyboard, mouse, and anything else connected externally. Then boot up. If behavior is normal for your mobo (correct error beeps, etc.), put in the RAM and test again. If normal, add graphics card. If normal, add more components; rinse and repeat. Sooner or later you'll connect something that will cause a problem, and you'll know what it is.
Sheep Rustlers in the sky! <S> Slapt | <S> FUI | Air Warrior II/III