If you experience same issue, you can follow below:
1. Remove any sim card in your phone.
2. Press power button and volume down till it shows Feedback screen. Just press Home, and it will show home screen. Try this for a few times.
3. You can now try to go to Settings > Devices > About > Reset your phone. This will delete everything in your phone, which I assume it should be OK as you already run beta software.
There is also other instruction on internet, which I have not tried: