Troubleshoot your device showing an exclamation mark on a black screen:
This screen is called recovery mode, and it is where an Android device provides options to help repair or install operating systems. Pressing or holding certain buttons during start up will bring up this menu, from the bootloader menu. Most Android devices use the volume up and volume down keys to navigate the bootloader and recovery menu, and they use the power key to select options.
The most common reason for devices starting up in recovery mode is that the device is rooted or has installed a custom ROM. T-Mobile does not provide any support for rooted devices or modified software, and you must refer to the device manufacturer for additional troubleshooting.
If you need help with doing any step, visit the Devices page, select your device, and find the steps.
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