Please ensure that you have the ActivDriver software installed and using the latest version (5.10.14), this can be downloaded from article 10902 on http://www.PrometheanKB.com. When installing/updating the driver please ensure your USB cable is not connected until after the installation has finished.
If you are still experiencing issues, please try powering off the ActivBoard at the mains for 10 minutes and powering back on. If the same issue, to ensure no cables are at fault, please test another known working USB cable directly into the ActivBoard bypassing any wall boxes or connection panels that may be in use.
If the issue still persists, I would recommend contacting Promethean Technical Support Directly.