New
#11
OK, I'll chime in...
Too many "weird" problems and I have had the same/similar situation in the past.
Your clue is "old system" - so, is this "old" as in perhaps the motherboard was one of the many thousands produced with faulty capacitors? What you describe sounds like what I experienced...all due to swollen (defective) capacitors on the mobo.
Open it up and look at all of the caps on the mobo. If any are swollen (barrel shaped) or the top is puffed out, that could be the problem.
Regards,
GEWB