Windows Phone Update Process Stuck? Try This
Courtesy of Microsoft, here's a process you can try if your phone gets stuck applying the update:
1. If backup process is in apparently prolonged state (exceeding the general 30-40 min) with no movement of progress (including stuck at 99/100%)
2. Disconnect the device from the PC
3. Pull the battery
4. Replace battery and power on
5. Device should reboot into the OSKernal
6. We would recommend at this time, not to retry the update, as subsequent attempts will fail similarly. While we continue to investigate the issue, we would ask that you not attempt the update until your device alerts you of another update opportunity, in approximately 3 days’ time.
7. Last resort option if battery pull reset does not work, instruct the user to consult their product documentation on Hard Resting the device to factory default.
If you run into this problem and these steps help, let us know in the comments!