Don’t Open your Facebook account upto 96 hrs. Clear the cache and stuff like history etc. It may be back to normal.
If you still can’t, go through the automated security verification process. May be Facebook has detected some suspicious activity and your account got locked. In such cases,
You can verify by confirming your mobile number. Facebook will send you a code, you need to enter and verify your Facebook account. Once you have verified, you may able to unlock your Facebook account.
Account authenticity: Facebook will give you an option to verify by identifying the photos of your friends. You need to identify at most five photos to unlock your Facebook account. You will be provided with two lifeline, in case you didn’t able to identify your tagged friend in one go.
Once you have succeeded in identifying the tagged photo of your friend, you will be welcomed with a message “Account verified congratulation!”
You have to click continue to proceed for the next step. You will be asked your current email address or you can go with your new email address.
You will be asked to enter a new security question. Enter your preferred security question and at last your Facebook account get unlock. Further, you can proceed with unlocked Facebook account by logging in.