Hi,

To remove the OSD lock, kindly use the steps as shown in the attached image:




Hope this solves your problem. Thanks for using FixYa.

Holding down the menu button for 10 seconds should work. Here is what I found online, which may be of help to you:
Hold the menu/ok button for ten seconds, to unlock the OSD.
If this doesn't solve the problem, then it's probably the button that got stuck.

if the monitor's still covered by the warranty, or if money is not an issue, have it repaired by professionals
If not, remove the casing, locate the menu button's contact switch on the circuit board, and try to release it using something thin like a screwdriver,
If this doesn't work, chances are the menu button is stuck on a loop, sending a continuous signal to the board (which keeps locking/unlocking the OSD).