I would of thought the one you purchased would of worked because yes you can plug the adapter in aslong as it has the correct voltage.
Have you tried taking it out of the case and rebuild it on the side case of the tower itself.
take it all to bits, and place it on the tower and rebuild it, try 1 ram, then 2, and diffirent one's if it still occurs , I'm sure you've done that already tho like you said..
take the harddrive out also.. if it still has it altho i doubt it's that
cd drive also
just use the motherboard, cpu +heatsink/fan, memory, power 20 pin in or 24 what ever you have and the 4pin also in.. nothing else needs to be in .. and use the onboard graphics which I'm guessing you already have