S2717DG Connection Issues

I have a S2717DG and I am having some connection issues. 

I have had them before but I cant recall how I fixed it. 

So I am using the display port which goes into USB. When connected via the DP I only get options on the menu to switch display to HDMI. When connected via HDMI the monitor operates fine. 

I have had the monitor working fine but have disconnected it and reconnected it recently due to a house move and now in the new house I cant seem to find the solution to get the monitor working again so I am confident that this set up worked fine, somehow my computer has forgotten how to use the monitor. 

I have looked at similar topics but I don't seem to be getting any joy. I have tried resetting to factory settings but no luck. 

Thanks