If you purchased a rental eBook, you will have access to the material for the length of the rental duration.
If you purchased an eBook with perpetual access or a rental longer than one year, online access via the web reader is only available for one year from the date of purchase.
This will allow you to download the content for offline use, where you will have access to it perpetually.
Note: be sure to sign in with your bookstore account; this should be your .edu email address. If you do not know your password, use the Forgot Password link to reset it.