|Do you mean the 'display adapter' entry is missing in device manager? Do any items show there with a yellow exclaimation or question mark? If so you probably need to reinstall the video drivers.|
If no hardware problems show in device manager then right click on an empty part of the desktop and choose 'properties' from the box that opens. Does 'display properties' come up then?
Did you make any changes to your system prior to noticing it was missing?
Could your video drivers or related software have created a separate entry in device manager that's called something else but does the same thing?
You can right click on the top line in device manager and a 'scan for hardware changes' box will open. If you do the scan it may pick up the adapter and show it again. You can also do the scan from 'add hardware' in control panel.
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