There are only two reasons why the Weather Radar will not work:
1. You do not have electrical power going to it (check the FE panel to be sure all electrical busses are turned on).
If you have checked and double checked #1, and the radar still does not work...
2. The installation of the 727 is faulty. Please uninstall, and reinstall using the Flight 1 eCommerce installer and your purchase key.