Problem using HDMI port on GTX 1660 Ti Mini GPU

[sacentre]

Can someone suggest what might be causing this problem, please.

I'm running a Dell UP2715K (5K) monitor from a Gigabyte Geforce GTX 1660 (6GB) Ti card. The monitor uses two of the three DP ports on the card.

I want to plug in a second Dell P2421D (2K) monitor making use of the HDMI port on the card. This is instead of using the HDMI Intel(R) HD Graphics 530 interface on the motherboard.

The problem is that when the second HDMI monitor is plugged into the GPU, my internal SATA CD/DVD ROM drive is no longer accessible and doesn't show up in Explorer although the disc access light flashes continuously. I tried disconnecting this and using an external USB CD/DVD drive in a USB3.0 port but the result was the same. However, USB thumb drives work fine.

I'm guessing this is something to do with drivers or config settings but I can't figure out why using an HDMI port should knock out the CDROM drive. Any suggestions would be appreciated.

Mobo = Gigaybyte Z170X- SOCFORCE, 32 GB RAM
GPU   = Gigabyte GeForce GTX 1660 Ti 6GB
Windows 64 Pro

[shadowsports]

Greetings,
This limitation has to do with the monitor requiring two outputs for 5K.  Its not the card or your system. 

To achieve 5120x2880, it displays 2560x2880 side by side.  The drive is disappearing due to lack of available resources. 

It might get fixed with newer or different BIOS rev or drivers, or it might never get addressed.