Turn off your pc, unplug it from your power outlet. Then push the power button a few times to discharge any remaining power in the capacitors. unplug any and all card readers (internal/external) memory cards, usb devises, flash drives, and mp3/ipod players. Wait a few minutes and plug the power cord back in. Turn your pc on without plugging any of the non essential usb devises and see if that starts your computer. if it does, restart and plug your usb devises one by one to isolate the one that causes the boot problems.