Facebook login can be pretty easy, but when you run into problems here is a great guide to help you get access to your account again.
1. Make sure your CAPS LOCK is not turned ON accidentally. Case-sensitive passwords on Facebook allow for Upper and Lower Case characters.
2. Make sure your email is spelled correctly and that you’re not accidentally using the wrong email address.
3. If you still can’t facebook login, then you can retrieve your password by clicking on the ‘forgot your password’ link and you will receive an email shortly after.