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If the Lenovo 40AY dock is missing some functionality such as display, but the ethernet and power still function it is more than likely a firmware issue.
Firmware 3.0..91 is a bad firmware that some docks may still possess.
To check a docks firmware download and run the firmware update tool. This is located at \\nefs.cecilcc.edu\Apps\Lenovo Software\Lenovo 40AY Dock old firmware
Click CHECK first to see what the firmware is. If it is 3.0.91 then you will need to revert the firmware to an older version. Run the attached firmware tool to flash version 3.0.57.
After the flash has completed you can run the Lenovo Commercial Vantage tool to run system update that will upgrade the dock to the newest firmware (currently 3.0.98.
Test the machine to see if display has returned and you should be good to go.