This is an unfortunate limitation of Dashboard. When the computer is restarted, it will not load any widgets until Dashboard is activated again. If you want to make sure Dashboard is loaded immediately when you log in, first open System Preferences in the Apple menu, then click the Accounts icon. Click the Login Items tab, and then click the + button below the list. Select Dashboard in your Applications folder, and click Add. Alternatively, you can use Dashboard KickStart.