Bootcamp suddenly stopped working.

So recently I have been using bootcamp and it has been working with no problems. But today it has suddenly stopped working. When I restart my macbook pro and choose to boot windows, it brings up the windows loading screen for a couple of seconds then just shuts down. Occasionally, it comes up with an error message saying windows did not start up correctly and gives me the option to continue on (which leads to the same shut down) or restart (which also leads to the same issue all over again).

There was an update for both Mac (which I have since installed) and for windows (which I have deferred a few times but now can't install because windows doesn't start).

I have some important stuff on windows, so any help would be greatly appreciated.