Dell U4021QW User Manual page 44

Use the Joystick to lock the button(s).
Press the left directional navigation of Joystick for four seconds, a menu appears on
the screen.
Select one of the following options:
Options
1
Menu Button lock
2
Power Button lock
3
Menu and Power Button lock
4
Built-in Diagnostics
44 | Operating the monitor
Select Option:
Description
Select this option to lock OSD menu function.
Use this option to lock power button. This will
prevent the user to turn off the monitor using the
power button.
Use this option to lock OSD menu and power
button to turn off the monitor.
Use this option to run the built-in diagnostics, see
Built-in Diagnostics.