When your Motorola XT 615 is frozen and not responding to your command you could hard reset it back to the default factory settings.
If you are going to sell the device you would also want to reset the device and remove all the existing data on it, because you wouldn't want a stranger to see your personal data and your friend's contact.
Note: If you wish to keep any data before resetting the device, then would need to backup this data onto the device or to your computer. There are two ways you can do this, it is either via the settings menu or via the hardware key combination.
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 XT 615 to reboot.
1. Turn off the Phone. Press and hold Volume Down button, press Power button.
2. Next the phone should go into Fastboot. Press on the Volume down key to select the Android Recovery option.
3. When you see an image of Android let go of the Volume down key.
4. Next open the Menu by tapping on the bottom right corner of the screen.
5. Now select Wipe data/Factory reset.
6. Then press OK.
7. On the confirmation screen, select Yes and OK to proceed.
8. Android will now begin to reset the device. When you see the "reboot system now", Press OK. If it is not selected by default make sure you select it.
Wait for your Motorola Motorola XT 615 to reboot and start itself.