Got one of these yesterday on the remote box:
07/03/2015 13:25:18 - System booted (Unknown 4)
I expect it was a crash.
Snap, I turned mine on last night. It booted up ok, waited for it to fully load so I could change the channel, but it wouldn't change, then I saw 'rebooting' on the front display channel. It was fine after than.
Funnily enough first the first time since I have had the box (tow years I guess) I had to turn it off at the back as it had locked up.....