Ann,
Is your OS 10.8 or above? If so, you will need to install our Beta driver. To do this disconnect all Promethean hardware from the computer. Go to Applications/ Promethean/ ActivDriver/ Uninstall. Restart the computer and select the link below. This will take you to the Community page where you can install the Beta driver for Mt. Lion.
community.prometheanplanet.com/.../42591.aspx
You will need to "Join" the group before you will have access to download the driver. Once the driver is installed you may reconnect Promethean hardware and the pens should now work. (case# 221540)
Thanks!