Windows Phone 8 is currently available on a number of higher-end smartphones. But one problem seems to plaguing a large percentage of Windows Phone 8 users: the random restart.
Windows Phone 8 users have claimed random restart problems on the Nokia Lumia 920 and HTC 8X models. And these aren’t random reboots that occur once in a blue moon. Some users claim that they’re occurring five or more times per day.
Windows Phone 7 featured similar problems until it was patched by an update. But despite there being dozens of pages of complaints on the official Microsoft forum, the company hasn’t yet responded to the issue.
Many of the problems revolve around the Lumia 920, the flagship Windows Phone 8 device released by the popular Finnish manufacturer.

If you’re experiencing this problem, then here are a few tips that might help to fix it:
-Power off your device and remove the SD card (if you have one). Some users report that the restart problem only occurs when an SD card is installed
-Don’t bother uninstalling apps to troubleshoot the problem. According to this thread, the problem isn’t related to any third-party apps or programs
-Wait for an official update from Microsoft (guaranteed to work)