It can happen once in awhile. I've been not-at-home the past few months and my mailserver fell over one day. I went to my apartment, turned it on, made sure mail was flowing, then went home. It had turned itself off again in the meantime. I drove out again, and turned it on, babysitting it for a few hours to see what might be happening. It's been up ever since, so, mystery. I would have liked a telephone/internet rebooter during all of this!