Well this just happened to my Nokia Lumia 822. As far as I can tell there was no rhyme or reason. I set my phone down for the night and turned on a couple of alarms for the morning. The next day I woke up, realized my alarms hadn't gone off, and went to check my phone. I hit the power button and it vibrated turned on, displayed the Nokia screen, and then displayed the "No bootable option found". Needless to say it looks like I am going to need a new phone.
Edit: On that note, what are my options as an on-contract Verizon customer? I do have their (Asurion, I think) insurance policy, but does that mean I would get a refurbished Lumia 822? I've had the phone for about a year and a half, so I'm sure all warranties are gone. I think that Lumia 822s have been out of stock for some time now, so how can I go about getting a replacement phone? I welcome any advice and suggestions. Was gonna stop by a Verizon store today.