Login page in PHP to be fixed (script)

The login page script needs to be fixed. When students register the site works fine, but when they leave the site and try to re-login with their password and username the login does not accept any of the information and does not allow any access to the [login to view URL] the students register they have the option of taking a psi class or psc class. The login should remember what class the student registered for and re-direct him to the proper chosen [login to view URL] I could use a better login and registration form design. All the script has been created, it just needs to fix minor errors.