What is in the URL after you try to login? Are you taken to any page or do you stay on the login page? If you have been denied access to a page you should see an access check variable in the URL.
If you are entering the username and password correctly and cannot login there might be an issue with the values you are entering or how they are stored in the db. Can you check your table in the db to confirm that you have a record for the user you are trying to login with? Also, are you storing the password in the db encrypted? If so you will need to ensure that you have the password column in your table set with a varchar of at least 40 in size to hold the entire password.