Psu + mobo + cpu/hsf.
Nothing else connected or plugged in.
Use a small metal tool to short the pins on the mobo where the power switch was connected for one sec.
If it does not power up your down to 3 parts.
Next step.....move the mobo onto a piece of cardboard and retest.
I had been testing a relatively old graphics card, after finding out the card was useless I had unplugged it from the PC. Of course making sure the power was completely off. When I had tried to turn on the computer, the power light would turn on and be stable, while nothing else would start up. Not a single fan or light would turn on outside of the power light. What happened and how do I fix this??
Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic