I recently had this problem, i pulled my phone out from my pocket and found i was unable to use the home or return keys. I shut off my phone and turned it back on to be brought to the bootloader screen. After playing around with my phone for a bit, i noticed that the volume keys were stuck pushed in. I unstuck the keys, turned the phone on again and came back on like normal. This is a possible solution for anyone having this problem. Hope it helps.