Well, a lot of cheapo powersupplies do this, and defective good ones. My old POS powersupply that came with my old case did that. The only solution was to do exactly as you say, hit the power after shut down. It was a PITA, and it only did it intermittnetly, so the dude @ the puter store wouldn't exchange it! I tried to get it to do it while I was in the store, but he just said if it happens that rarely, it's gotta be the mobo. Oh well, I got a new case with an enermax PSU, and it never happened. I'd either swap that PSU for another, or spend some more if it's a cheapie, and get a better one. Good luck, hope that helps.