The Sugar MTK software tool downloaded and installed on your PC.

: A failed security update or a system error can leave the operating system "missing" or unbootable, forcing the device into the bootloader by default. Battery Issues

If the device remains unresponsive to restarts, you may need to reload the software: BlackBerry KEYone (BBB100-1) - Reset Device - AT&T

How to Fix a BlackBerry KEYone Stuck in Bootloader Mode A BlackBerry KEYone stuck on the bootloader screen (often showing a black screen with technical text, an Android mascot, or a "Fastboot Mode" warning) can happen after a failed update, software glitch, or custom modification attempt. This guide provides a systematic, step-by-step approach to safely reviving your phone. Step 1: Perform a Forced Hard Reboot