My PC mysteriously turn itself back on

[pink_angel]

hi....got another problem here...recently my pc began to mysteriously turn itself back on after I turn it off....I checked if my pc got a trojan, or virus through my anti-virus which I always update and even downloaded a spybot to see if there are any spywares, my anti-virus and spybot didnt find any so i asked a friend of mine to check on the BIOS setting, and he said everything is just ok...I already replaced my power supply and its still the same....what could be the cause of the problem....

btw, my motherboard is AMD and I dont have those WOL(wake-on-lan) thingy...

thanks a bunch!!