If you're using the Security Wizard, always edit the WID box and match what you type here to your database name. This way you won't get confused between workgroups. Also, do not check the "I want to make this my default workgroup information file". This will make it the wif that Access will use with every database.
Access is installed with a default wif called system.mdw It's better if you leave this alone. However, if you did mess with it, you can either reinstall Access or just copy a System.mdw from another computer.
You can delete any .mdw's, but Access needs at least one to use. It's called Jet Security and it's "on" all the time even if you don't know about it.
Neil