the phone only shuts down when not in use, and not plugged into a power source. It fell decently hard, but there seemed to be no external damage. The phone was unresponsive right after the fall, but booted up a few minutes later. It works as well as ever when I'm making calls, browsing etc. but if it is left without being used, it will always turn off after a minute or so. What happened, and can it be fixed?