My desktop PC running Windows 7 with Gigabyte motherboard keeps turning on spontaneously. I put it on sleep, then come back a few hours later, and it's on. I have verified that no one else used it. My keyboard and mouse are able to wake the computer if they're used, but no one is using them, and they haven't caused this problem in the past. I've had the computer for a couple of years now; this problem has just recently started.