Please check your keyboard brightness settings by pressing FN+F8 on the Streak or FN+F6 for the miniStreak. FN does not need to be held if the FN_lock is on.
Please note: On-board lighting adjustments (Fn+F5/F7 depending on Streak/miniStreak) are purposefully deactivated if Fnatic OP software is open (or is a background process) on your PC.