Windows was working, but now boots to a black screen?

I had windows 8.1 working completely fine on my MBP (2015, 15 inch) but now upon booting to the windows partition, I get a black screen. No cursor, absolutely nothing on it. Pressing F8 does nothing to get safe mode (even tried an external keyboard). It seems to do absolutely nothing upon booting other than the startup sound. The only way for me to get a functioning computer is of course to hold ALT and choose to boot to OS X. I really really don't want to reinstall windows, does anyone know anything I can try to repair it?