Maybe you have been accidentally logged out or you didn't log into your account. You can check this easily by looking at the top right corner. If there is a profile icon visible, you are logged in. If you can see the blue button saying 'Log in', you are not logged in. Click that button to log into your personal Symbaloo account.
If you haven't created an account and you can't see your personalized Symbaloo webmix anymore, you unfortunately lost your content and you will have to start over. It is possible to use and personalize Symbaloo without having an account, but the settings are stored in the browser cookies. If these are deleted, so are the Symbaloo settings. Make sure to create an account and always log in before you make changes to your Symbaloo. This way you will never lose anything. Your settings, tiles and webmixes are securely stored in the cloud.