To the best of my knowledge the NASTAR software does not support running time in dual mode. The times freeze at the finish. Try using the software in single course mode. Select "ALGE" in setup and test. Set your display on rotary dial 0 with the toggle in the center.
If that does not work than there is an issue with your software. Uninstall it and try again.
ALso try downloading the "SKI CLUB" software from
www.splitsecond.com It is very similar to NASTAR and will let you test the display for 2 minutes.