WD19TBS and Three monitors

Hello

I have a work setup I need help with. I have a Dell Precision 7740 connected to a WD19TBS docking station with two active U2412M monitors. Previously I had the previous version of this laptop with a click in style docking station using three of these monitors (laptop closed). My problem now is my laptop or docking station is not recognizing the three monitors. Just two (with the laptop closed). If I open the laptop it will adjust and recognize three displays. What do I need to do to have the computer recognize three external monitors while closed? The two that are working are connected via displayport and the one that is not working is connected via HDMI. 

Thanks