there is a possibility for confusion here
have you set a passwo4rd on the database or have you been tinkering with the workgroup file(s).
I don't use passwords on Access DB's but I do use workgroups, so my comments refer to workgroup problems
workgroup files can be PC specific (but thats a pain to maintain and administer), they can and should be networked, or you can use both local and networked if required by specifying the appropriate workgroup as a command line switch when opening access usually you'd do this as part of a desktoop shortcut..
all is not lost, Id suggest you open Access then attempt to rejoin to the local workgroup file (its in the tools / security settings).
then open up your copy of the problem app.
if that fails then you may need to open Access with a specified workgroup file.. have a google for Access command line switches