It may be that the graphics card is not powerful enough for the full resolution. What resolution do you currently have and what graphics card are you working with?

For information: ONLY a USB-C to DVI cable works, all other inputs on the monitor are not suitable for more than 3840 pixels by standard.

I will probably have to send this monitor back too: On the new MacPro with Radeon 580X (can drive two 5K monitors) with HDMI only 3840 pixels, everything blurred and not for working! Thunderbolt 3 cable on USB-C connection no picture. Now I have ordered a USB-C to DVI cable. I don't think that works either... In my opinion, the monitor is only intended as a double 27 inch monitor, but I have two LG 38 inch monitors for that purpose, so this one is no advantage.