1. Switch off your phone, and disconnect the charger.
2. Press and hold the volume down key, and connect the charger. If an exclamation mark (!) is shown on the screen, release the volume down key.
3. Then press the volume and power keys in the following order: volume up, volume down, power, and volume down.
4. Wait for your phone to reset, during the reset you will see gears rotating on the screen for up to 5 minutes, after which the screen goes blank for ~30 seconds and then your phone will restart.
5. Go through the initial phone setup. Make sure that you have the date and time set correctly on your phone (Settings > date+time).
6. Disconnect the charger.