Connecting a Dell Optiplex Moniter to Mac Mini i3 A1993 2018

In this case I am sure that the Mac i3 is functioning and that the Dell Optiplex Moniter is also functional; there is no USB port on the Moniter.

Previously I had an Apple A1347 Mac Mini running with a Vodafone Router and I am using the same cables now, but there is no responce from the Moniter, the Dell Self Test only appears and moves around on the screen.

The ethernet cable is functioning on my PC and I also use a Net Gear Prosafe GS105 with cross over cables on the PC.

I now have a Shell Energy Router DGA0122NLK and I am not absolutely sure if I am using the correct ports on it as not much details were sent, but it works for my Viglen Genie PC.

What I realy want to do is get the Mac Mini, Coffee Lake running the PC is only a server computer in this situation.