User cannot login into Salesforce

Issue:
An user cannot log in Salesforce.


How to resolve:


1.) Check if the user is using the correct URL.
2.) Check if the user is using the correct User Name and Password for that environment.
3.) Check the user's login history, navigate to:
      -  Setup => Manage Users => Login History
4.) Check if any login on hour restrictions or login IP address restrictions exist on the profile to which the user belongs, navigate to:
      - Setup => Manage Userd => Profiles => Login Hours
or
      - Setup => Manage Users => Profiles => Login IP Ranges
and check if there is any restriction.