A friend of mine bought some components and had not built a computer before so he brought them over and I helped him put it together. We put it together, hit the power switch and nothing. I suspect a bad motherboard, but I know thats a common thought when things don't work initially, and most of the time its incorrect. So here is what we did to try and troubleshoot it. Unplugged the PSU from the motherboard, and shorted out the green wire and a ground. PSU fan spun up. So figured PSU is ok, but I know thats not always true because I've seen bad ones do that too. Tried known good PSU from my collection. Removed the power switch headers and tried shorting with a screwdriver incase I put the wrong wires on the headers. (The case he's using is one of my old ones and its got all individual wires rather than the nice block to put on the headers, so I thought maybe it was possible I made a simple mistake). Removed the motherboard from the case, to eliminate a short somewhere. Reset CMOS. Removed the RAM (this was a longshot I know) So in summary, I think I've ruled out the following: Bad power switch or incorrectly wired power switch. Bad PSU. Short between the mobo and the case. What have I missed? Hardware involved: Corsair CX 500 PSU ASRock H61M/U3S3 Mobo Intel i3-2100 Patriot Signature Line DDR3 RAM (2x4GB) No HDDs or Optical drives connected at this time.