How to Fix a Locked / Unresponsive OSD Menu on the AOC Q27G2

The OSD control lock is enabled — the Q27G2 has a built-in OSD Lock feature that disables the menu/joystick so settings can't be changed accidentally. It's easy to trigger by holding the joystick down for a few seconds by mistake, after which the menu won't open at all and the monitor appears to have broken controls.
The joystick is stuck or its switch is clogged — the Q27G2 uses a single clickable joystick for all menu navigation. Dirt, dust, or a physically jammed switch can make it unresponsive or cause it to scroll on its own, so the menu acts locked even when the software lock is off.
A crashed OSD overlay — like any embedded menu, the OSD can hang after a signal drop, graphics-mode change, or rapid joystick use, leaving a frozen or blank overlay that ignores input until the monitor is fully reset.
Monitor firmware bug — occasional Q27G2 firmware revisions have reported OSD freezes or the menu refusing to respond until a power cycle, especially after FreeSync/Adaptive-Sync or Mode toggling.
Conflict with AOC G-Menu desktop software — the AOC G-Menu utility drives the OSD from the computer. If it's holding settings or has crashed while adjusting brightness/overdrive, the physical OSD can appear locked or fight the software for control.

Unlock the OSD — on the Q27G2, press and hold the joystick/center (Menu) button for about 5 seconds. This is the toggle for the OSD lock: holding it disables the menu, and holding it again re-enables it. If the panel was accidentally locked, a single long-press restores the controls.
Power-cycle the monitor — turn the monitor off and unplug it from power for 30 seconds, then plug it back in and turn it on. This resets a crashed or frozen OSD overlay and clears any stuck menu state after a signal or mode change.
Clean or reseat the joystick — with the monitor off, gently work the joystick in all directions several times to free a stuck switch, and use a dry cloth or a light blast of compressed air around the base to clear dust. If it's physically jammed and won't click, the joystick assembly may need service.
Close AOC G-Menu and adjust via the OSD — quit the AOC G-Menu desktop application (and any monitor control software) from the taskbar, then try the physical OSD again. If the controls respond only after closing it, G-Menu was holding the settings and you can reinstall or update it.
Update the monitor firmware — check AOC's support page for the Q27G2 and download the latest firmware if one is listed. Flash it per AOC's instructions to resolve OSD freeze bugs, then restart the monitor. If the OSD still won't respond on every power cycle, the joystick or control board is faulty and the unit should be handled under warranty.