On some monitors, there is a Power Button Lock that locks the power in the ON position.
There is also a menu lock feature which can lock and unlock the OSD.
Power Lock: To lock the Power button press and hold both the  button and the down arrow button for 10 seconds.
OSD Lock: To lock the OSD press and hold both the  button and the up arrow button for 10 seconds.
Note: These same buttons, when pressed for another 10 seconds, will unlock the feature.