All computer monitors, whether they are LCD or CRT style, have a built-in feature called the on-screen display (OSD) lockout that prevents users from viewing any images on the monitor. If your computer screen has accidentally been set to the OSD lockout setting, there are several ways you can remove the lockout.
Power off your computer and then remove the monitor cable from the port on the back side of the computer case. Reattach the cable and make sure the pins are correctly screwed in. Power the computer back on and check to see if the OSD lockout message is still being displayed. Check the manual that came with your computer or monitor and locate the troubleshooting section if you are still receiving the OSD lockout message. Find the OSD lockout heading and read the method that your particular model uses to remove the lockout. Attempt generic lockout removal procedures if you no longer have the manual that came with your monitor. Press and hold the "Menu" button located at the bottom of your monitor for 15 seconds and wait to see if the OSD lockout message disappears. Press the "Menu" button again if the lockout message remains on the screen. Use the arrow buttons to navigate through the main menu options. Highlight the "Settings" or "OSD Menu" option and then hit the Menu key again to access the new list of settings. Scroll down to the "OSD Lock" heading. Use the arrow keys to change the setting to "No." Hit the Menu key again to return to the main menu. Scroll to the "Exit" setting and then hit the Menu key a final time to exit the menu setting and remove the OSD lockout.