Documentation - Require Login
To enable Require Login for NRO, select System / Configuration / Customers / Customers Configuration > Login Options and change Require Login for Access to Yes.
Using Inline Translation
Because of the way access to the site is locked down entirely, you can't use the Inline Translation feature on the Account page when Require Login is enabled. To make Inline Translation changes to the Account page, you must first disable the Require Login feature, make your Inline Translation changes, then re-enable the feature. When making Inline Translation changes on any page other than the Account page, you can simply log into the site and make changes as normal — only the Account page is locked down completely.