Black screen external monitor

Please let me know if this issue belongs somewhere else. I'm using a Surface Pro 2 using a fresh install of the latest stable build. The internal monitor is working fine, but my 2560 by 1440 Dell U2518D is not. The monitor shows up in Settings>Displays and I can move the mouse onto the area where it would be, but the monitor just shows "No DP signal from your device" and stays black, but on. The display works perfectly under Windows, and I have tried a number of solutions already:

- Deleted monitors.xml
- Unplugging and replugging while the cable is connected, and not connected
- Rebooting with the cable connected and not connected
- Looking for a new Intel graphics driver (this seems to be baked in though so everything I tried was already installed)
- Changing the resolution of the external monitor
- Changing the refresh rate of the external monitor
- Disabling the external display, and separately, the internal display

This installation was done using the whole drive, encrypted on installation, with these device BIOS/UEFI settings: Secure Boot turned off, TPM on.

I noticed that turning the monitor off at the wall, then on again while the DP cable is plugged in, the wallpaper shows up for a split second on the monitor, before it turns black again.