I have been using dual displays with my Surface Dock and Surface Dock 2 for awhile now, but recently the second external display would just go to sleep and not display anything no matter what I tried.
The solution was found in a Microsoft forum.
Clear your display cache.
- Undock your Surface from the Surface Dock.
- Download the Surface Dock registry file. Choose to Open the file.
- Select and run surface dock registry.reg.
- Select Yes to allow changes to your Surface, select Yes to confirm, and then select OK to close.
- Restart your Surface, reconnect it to the Surface Dock, and try your external display again.