Can you check what firmware you have on the MST Hub? It is located on the cable with a white sticker. The latest version is FW 0.45
Also please tell us what MST Hub model you have.
Check if you can power off completely the system, that means also taking off the power cable out of your power supply, drain the system power by pressing the start button.
Make sure that you have the latest Nvidia Quadro driver in your system