Dell D3100 Dock not working
 

I have a dell D3100 dock hooked up to 3 Asus monitors. I recently added the third monitor into the displayport. Slot previously I had no issues. Now I am having the issue of the monitor hooked up to the displayport slot goes blank, turns purple , sometimes white and then freezes both my other monitors. The only way to fix it is to unplug the laptop and then re-plug it back in. This makes it a basically unusable set up. It happens at randoms times. Sometimes over 10 times in a few hours. I have tried different monitors, replaced the dock once, uninstalled and reinstalled drivers and nothing has worked. Does any one have any suggestions.? I don't understand why its having so many issues.

Also this happens with two different laptops that I use on the set up. Both being dell computers running Windows 10