DIAGNOSIS The single multi-direction joystick/button on the back or bottom edge controls the entire On-Screen Display (OSD) menu. It's not intuitive if you're used to dedicated buttons.
FIX Press the joystick directly in (like a button) to turn the monitor on/off or bring up the OSD. Once the OSD is up, push the joystick left/right to navigate between menu icons (Brightness, Volume, Color, etc.). Push it up/down to adjust the value for the selected setting. Press it in again to select or back out of menus.
IF THAT DIDN'T WORK The joystick can be finicky. Make sure you're pressing it straight in. If the OSD is unresponsive, the monitor might be locked in an input detection mode. Unplug all cables, wait 30 seconds, and plug just power back in to see if the OSD works standalone.
HEADS UP The brightness setting in the monitor's OSD is separate from your laptop's brightness keys. You often need to adjust both. Also, the OSD usually times out and disappears after a few seconds of no input, so don't think it's broken.