It really does sound like your not getting enough juice to the system. You would get the same sort of things happening to a pc with a old or new "cheap" PSU.. not all psu are equal.
I had a $250 850W psu in a new system i built and everything was running slow and hanging (the 12V,5V and 3V were very low) i changed it with a more epensive (enermax) 850W psu and everything was fine.
My own A1200 had prob with power until my friend redid the AT PSU that i had it plugged into.
