Docking station issues

I have been having issues when I dock my Latitude D630 into the port replicator. The issue is that sometimes the external monitor is not detected and therefore, doesn't display my screen. I tried using the fn + F8 to extend it but in the display properties, the monitor isn't even recognized as being there. I was initially having intermittent issues with keyboard and mouse so I swapped docking stations and now this came up. 

Any suggestions what I can look at? Could it be something to do with the hardware profile?

Thanks