If you're repeatedly asked to log into My Account (or receive repeated messages that your validation has expired), this is generally a symptom of either not having cookies enabled in your web browser or a third-party application is blocking cookies on your computer.

Overview
In order to log into My Account, you must have your library card number and PIN.

Once you have authenticated with My Account, a cookie is set on your computer to indicate that you have successfully logged in. This cookie allows the library's catalog to maintain your My Account session.

Thus, cookies are required to use My Account and must be enabled.

To learn how to enable cookies, please try searching Google.
You might also try to clear your cookies to fix this problem.

*What's a Cookie?
A cookie is a piece of text that a web server can store on a user's hard drive. Cookies allow a web site to store information on a user's machine and later retrieve it. The pieces of information are stored as name-value pairs. Cookies are required for the library's catalog to recognize that you have logged into My Account and help to maintain your session.