Read this FIRST before posting

All Apple macOS users should read through = FAQ Dell monitor and Apple

(1) First, check the sticky FAQ Monitor. It has many topics that could address your issue

(2) Where do I find my monitor Service Tag number?

(3) No cables, power button reset
* Turn the PC off
* Turn the monitor off
* Disconnect every cable (including the power cable) from the monitor
* Press the monitor power button in for 8 seconds (clears any residual power in the circuits)
* Reconnect the power cable to the monitor
* Reconnect only ONE video cable from the monitor to the PC
* Turn the monitor on, then the PC

(4) Run the monitor Reset, Self-Test, BID (Built-in Diagnostics)   
 * Take and post pictures of all of the monitor BID (Built-in diagnostics) colored full screens showing the issue
- If the monitor fails the Self-Test and BID and is still under the purchased 3 year warranty, see this

- If the BID passes the Self-Test and BID, the monitor itself is functional. The fault lies with either the cabling, video card/GPU, video card/GPU driver, or operating system

(5) Post your issue in public on your own thread with all of the following data
* The specific issue and all troubleshooting done
* What PC model?
* What GPU/video card is installed in the PC?
* List all of the available video out ports on the GPU/video card or PC itself
* What operating system?
* What specific monitor model?
* Explain how the monitor is connecting to the PC using which ports and cable
PC GTX 1080 DP out port --> U2718Q DP to mDP cable --> U2718Q mDP in port
PC USB port --> U2718Q USB upstream cable --> U2718Q USB upstream port

(6) How to initiate an in warranty monitor exchange
Right of your public Post, click the blue Get Help Now button. This will start a private Chat with a Dell agent. Provide the following private data to the Chat agent =
* Explain the issue and all troubleshooting done
* A picture of the monitor label showing the private Service Tag and 20 digit Serial Number
* Picture of the visual issue
* Pictures of the monitor when running the stand alone BID (Built-in Diagnostics) showing the visual issue
* Your full name, shipping address, phone, email address
NOTE = If you did not purchase this monitor directly from Dell, they will also need a picture of the reseller invoice showing your data and the purchase date. You also have to first fill out the Ownership Transfer form