Cannot login to a MS Access database
Instead of looking for matching username and password from the table, I would suggest you to use login system explained in this link. You just need to import forms and code from demo database from the link into your DB. You'll also get password change form and password reset option. I've use the same approach in my project. I also adopted (recommend you to do too) storing encrypted password approach to prevent user password in case the DB is compromised. If you need any help in that regard too, I'll be happy to help.