When it feels like it, my PC decides to just keep restarting itself instead of actually booting up. I turn it on, it fired up, fan kicks in, then goes off as normal, just as the manufacturer screen goes it starts over again! I unplug it, try again. Fires up, fan kicks in, won't switch off. Unplug it, try again, then it's fine! Does it say, once a week? But I have no idea why! Took the case apart and gave it a good clean inside, all dust free etc, but it still does it. Any ideas?