Lately, my computer has been shutting down randomly. When it shuts down, I can't reboot it unless I unplug the PSU and then plug it in again. Whenever it is about to shut down, my HD makes this sound like it's powering down, similar to when I shut down the computer manually. Is my HD on its last legs? It's a 6 year old Maxtor, so I could see it dying fairly soon. I don't have the computer overclocked right now, but it was in the past.