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The OSD Lock can be Locked or Unlocked by holding the OSD menu button (A) for15 seconds after powering the monitor on.
This information was buried and VERY difficult to find.Never seen this behavior before.
Note: You can also lock or unlock the OSD by pushing the Menu button (A)for over 15 seconds.http://support.dell.com/support/edocs/monitors/1901FP/en/controls.htm
Report Unresolved Customer Service Issues here I do not work for Dell. I too am a user. The forum is primarily user to user, with Dell employees moderating.