Switch off your computer completely and then disconnect the monitor cable from the port.
Reconnect the cable and be sure the pins are properly screwed and are connected into the correct port.
Switch on the computer and check whether the OSD lock message still appears on the screen. If the OSD locked still reappears, proceed to the next step.
Refer to your monitor user manual and particular under the OSD unlocking procedure and follow the instructions carefully.
If the manual is no longer available, then try the generic lock out removal procedures, by pressing the "Menu" button of your monitor for about 15 seconds and wait for the OSD lock out to message disappears.
Press the arrow buttons and surf through the menu options. Select the "Settings" and then press the Menu key again to access the list of settings.
Scroll down and select the "OSD Lock" Option. Use the up and down button to change the setting to "No." then press the Menu button to exit return to the main menu. Go to "Exit" option and then press the Menu key to exit from the menu setting and remove completely the OSD lock out.