Trying to open Fastboot on a reluctant Priv is frustrating. Ensure these conditions are met:
Although the Power + Volume Down combination is the standard method, some users have found success with these variations, especially on older software versions: how to open fastboot mode on blackberry priv hot
Type the following command to verify your connection: adb devices (If you see your device serial number listed, your connection is secure.) Trying to open Fastboot on a reluctant Priv is frustrating