This is the most reliable method for the BlackBerry Q5. It involves using a PC to flash an older version of the OS (typically 10.3.1).
A for version 10.3.1 (e.g., SQR100-1/2/3). A high-quality USB cable. Step-by-Step Instructions:
for the process to reach 100% and for the device to reboot automatically.
When the program displays connect your Q5 to the PC via USB.