Jayne,
Try and connect a USB keyboard and press CTRL+ALT+DEL. This will take you to the Windows account. Go to Start > Log Off and log back into the ActivTable account. If you are still having issues, please contact Technical Support via the web form on the knowledge base at www.prometheankb.com, select your region/language, Interactive Displays, Contact Us. In the Existing case field input case number: 276576 and include the ActivTable serial number.
Thanks!