Set the Account Login Module as visible to Unauthenticated Users Only

By configuring the account log in module as visible to Unauthenticated Users only, the module will not be displayed once a user logs in to the site. In order to proceed you need, when logged in as an administrator, to mouse over the arrow beside the title of the module.
 

Select Settings. Or click the icon  at the bottom of each module.
At Permissions check, under the View Module, Unauthenticated users.