FB is doing more upgrades so when that happens there are always major problems for some folks. It can be a royal pain in the patootie. Once they get the bugs worked out then there won't be any major problem. The biggest issue is in the past it has taken them upto a month to fix all major glitches. I really don't know what to tell you besides to clear history, cache, cookies etc and then reboot your browser and try to sign in again. Good luck.