S2719DGF, no HDMI 1 (1.4) signal, AMD Radeon R9-200

I am a rookie here.

Just bought and installed the S2719DGF Dell monitor.

The display seems very tiresome to my eyes.

But maybe it has to do with the HDMI connectivity / settings.

When I shut the pc down I get the message "no HDMI1 (1.4) signal from your device".

What is that supposed to mean? That the pc is off, so no signal is being sent?

That there is a connection problem? But the S2719DGF is functioning.

Does it have to do with my graphics card? (AMD Radeon R9-200)

Please help!