I'm pretty stumped by this one. I was going through the process of flashing my router, and I found that when I disconnected the internet it would, after a short moment, crash to reboot. From there, it would go into a reboot loop until after about three times of not even making it to the start screen, it'd give me the recovery options. The only thing that seemed to fix it was a system restore--unless I reconnected the internet somewhere along the way, then it would usually boot back up.
I've done it a couple of times now (in the name of science), and it's definitely related to having a connection or not. This didn't ever happen before I upgraded to 8.1. Any thoughts?