My expensive Iiyama ProLite XB3270QS monitor got stuck and no matter which button I pressed, the stupid error message "OSD Locked" kept appearing and I could not adjust the settings any more.

This has been going on for days now, and I had finally accepted the fact that I would have to switch my two computers manually to the monitor by using separate HDMI cables, what a pain.

Turns out that the solution is pretty simple. According to the online manual, "The power switch lock will be deactivated by pressing the front buttons MENU and › about 10 seconds."

Lo and behold, it works!