PC will not boot up

Pc would restart automatically, then would not start up at all. No power to system except for one red light inside. Replacement 400 watt supply would not work. 230 Watt from another machine worked but error message “missing file D007? Not sure of message. Now no boot up, black screen, but power supply is on. No sounds from hard drive. Formatted HD and reinstalled windows on another machine. Still nothing. Is it the Motherboard? CPU? How do I troubleshoot these? Bad one is an AMD 1.7 G and the other running PC is a PIII 450.