It's possible it may just something particular about your motherboard, not saying there is something wrong with it. My kid's pc has a MSI K7T Turbo in it and it does the same thing. If I pulled the power for whatever reason, then I plug it back in or flip the switch behind the Power Supply, it will boot up. I have changed power supplies before and it still did it. I put computers together for a side business and I've noticed several motherboards do this. Everything works flawless with all the motherboards, probably about 5-6 different ones, so I never complained.