500 or even 600 watts is completely ridiculous for that kind of setup - with just one harddrive 200-250 watts will be ample.
As has been said: check cabling - a single thin wire won't do. Check voltage levels on various parts of the board and CPU card.
Also check for caps failures: electrolytic caps age, lose the capacitance and may leak. Check for bulged tops, blown rubber stops and brown residue.
