you might want to check once more, remove any pci/pci-e from your pc
in some case, PCI lan card prevents pc from powering on. it could be graphic card or something in pci-pcie
btw if you have time.....
this one is really long tips but it can save you from getting headachehttp://www.tomshardware.com/forum/261145-31-perform-steps-posting-boot-video-problems