Anytime I have issues with something like this, I start but unplugging things (but keeping track of where they were plugged in) and getting just down to motherboard, one stick of ram (if there is two or more), video card (if needed), and the CPU. Older machines should have a speaker on the mobo so wait for a beep if there is a speaker. If it posts then, start adding things back in and see where it fails again.