Hi there my phone just did the ezact same thing. However i held down the power key and down volume for 30 seconds even when the screen goes off and its turned back on, lets me put in my passcode again now. Although the phone is still playing up, and telling me facebook has suddenly stopped, But i hope it helps you to recover your data before maybe doing a hard reset.
This happed to me last night, id restart the phone ( hold power button and volume button) it would work normally for a while then came up with "Facebook is not responding" and my phone screen would freeze then turn black so i restarted it again, once i unstalled Facebook my phone is working normaly again.
Mine has been doing the same since Facebook updated a couple of days ago. I can't gt in to FB, uninstalling and reinstalling multiple times hasn't helped. Keeps saying it is unresponsive or has stopped. FB messenger won't work either. Now other apps are having issues, including time hop and pinterest. The phone randomly decided it was 2.30am overnight, causing me to miss my alarm and sleep in. It wouldn't unlock, it wouldn't turn off, no calls coming through. I googled on my laptop and found how to do a hard reset - press and hold the power button for 30 seconds! Facebook and messenger still not working, phone freezes and needs hard resetting about 6 times a day. Sounds like a common fault this week with these phones. I will have to take it to the store
I went into the Vodafone store today. All they can do is uninstall FB and Messenger. They took my details and will call when a new update for Facebook comes out. So if everyone would like to save a trip into town, this is the best option. =)
Vodafone is liasing with Facebook because the guy in the store said this phone is available globally. So it won't just be us.
Hope this helps.
In the meantime, it's gotten me away from Facebook pretty good. Lol.