Here are simple instructions that you could use to perform a hard reset of the Motorola XT390.
When your device is not running as it should because it has frozen, then you could reset it back to the default factory setting. However you should backup your device first if you would like to reused some of the data you current have on your device.
You can use the setting menus to reset if your device is not frozen.
1. Go back to the Home screen.
2. Next tap on the application list.
3. Select Settings.
4. Then choose Privacy.
5. Next tap on Factory data reset.
6. Then select Reset phone. If you want to wipe out all data on the SD card then make sure the checkbox Erase USB storage is ticked.
7. Next follow the onscreen instruction to finish off the process.
Wait for the Motorola XT390 to reboot.
Crash Recovery Reset - With this option you will not lose data.
1. Take out the battery and leave it for a while, then put the battery back and restart your phone.
Also try the hardware key:
1. Turn off the phone.
2. Press VOLUME UP + VOLUME DOWN + POWER KEY for a few seconds.
3. From the Boot options screen, use the VOLUME DOWN key to navigate to the next option, then select the Recovery by using the VOLUME UP key.
4. When you see the Motorola logo screen, press the VOLUME UP + VOLUME DOWN key.
5. On the next screen, press the VOLUME DOWN key to go to the Wipe data / factory reset option, then use the POWER key to select that option.
6. Press VOLUME DOWN key to select YES - delete all user data. Then Press the POWER key.
7. When prompted for a reboot, press the POWER key.
8. Wait for the Motorola XT390 to reboot.