With no hard drive it is not going to be software. Fiddling with software is the no dollar cost starting point.
I can not imagine the video card, RAM, or processor causing this but anything is possible. Re-install all the parts and check the case and cables for shorts or wear. This is a long shot but, again, zero dollar cost.
You already cleared the CMOS so the next step would be to try re-flashing it. Maybe fall back to an older firmware then back to whatever is good and current for you mainboard.
I am not quite sure what you said about the PSU. Are you using that crap 200W? A P133 PSU should not even be compatible with this system. Do you have or can you borrow a PSU tester? If the PSU is gone squirrelly then the next thing to do would be replace it.
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Companion - E8400 - P5K SE - EN8600GT SILENT - 2x1G Ballistix (POS) - WD250 - X241W
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