* What specific Desktop PC model?
* Using what cabling and ports on both, how is the UP2516D connecting to the Nvidia Quadro M4000?
* You stated, "DUCCS used to identify the UP2516D correctly", so what did you change just prior to it not identifying it?
* Have you tested the UP2516D on a different PC and installed its driver to verify that it shows up in the Device Manager- Monitors. Then tested DUCCS?

• DDM does recognise the monitor correctly
• Device Manager does recognise the monitor correctly
• UP2516D is connected to Quadro M4000 via a Display port to Mini Display port cable
• PC is custom made. 
• I have no other desktop PC.
• I identified the issue after installing Davinci Resolve 15. This program messes up several display related settings. But it might have been caused by an update in Windows, not sure.

Hey guys anybody know what this is all about?

Problem persists. Any Idea? All other aspects of the monitor seem to work fine.

After resetting my UP2516D to factory settings, I suspect my firmware defaulted to the original one. Is that a fact? I am running the firmware updater. It tells me that it cannot detect the monitor model and the current firmware. I am connected with a USB cable (from the bottom ports of the monitor) etc. DUCCS and DDM have been uninstalled. There is a USB selection which blanks out when the USB is plugged, maybe those settings have something to do? What might be going wrong?

Click my username and via private message send me the monitor service tag number.

The Menu- Others- Factory Reset cannot "change" the firmware. It just removes your custom calibrations.

The only DUCCS validated for this monitor was version 1.5.10.

Test using the UP2516D USB 3.0 upstream cable on all of the PC USB 3.0 ports.

As to why the firmware will not allow you to install over itself, unknown. Have the Firmware Update Instruction PDF open to make sure you are doing it correctly.

After resetting my UP2516D to factory settings, I suspect my firmware defaulted to the original one. (Am I correct?)

I am running the firmware updater. It tells me that it cannot detect the monitor model and the current firmware.

I am connected with a USB cable (from the bottom ports of the monitor) etc. DUCCS and DDM have been uninstalled. There is a USB selection which blanks out when the USB is plugged, maybe those settings have something to do? 

What might be going wrong?

Also, Device manager properties display that the device (monitor) requires further installation. 

Driver version says 1.0, not sure this is right. Got the drivers from the dell site

* Click my username and via private message send me the monitor service tag number, 20 digit serial number, A0x revision number
* As I already stated, the Menu- Others- Factory Reset cannot "change" the monitor firmware. It just removes your custom calibrations.
* You must be using DUCCS 1.5.10. Is that the version you are testing now?
* Did you test the UP2516D USB 3.0 upstream cable on every USB port on the PC?

As a courtesy to the users of this forum, I inform that the problem with updating my firmware was caused by me using a USB 2.0 cable to connect the monitor to the PC. A USB 3.0 cable is required.

Now is there anybody else here whose monitor is not recognized correctly by DUCCS?

Thank you all, 

After a long time, I managed to resolve the issue by clean installing the Graphics Card drivers. The idea came from the XRite helpdesk. THANKS FOR NOTHING DELL!!!!