Duh, incorrect or corrupted CMOS settings can prevent your PC from booting up. Resetting it restores the settings to factory-defaults. The message "Overclocking failed or Overvoltage failed!" was the clue, because incorrect Overclocking results in symptoms similar to what you described.
It definitely sounds to me like capacitor(s) are failing, check them again with a bright light and make sure you get a good look around the bottom of them for leaking electrolyte (brown/greyish). Take the board out if necessary.