First, please check that you are connecting the coaxial cable into the proper RF port. On the Digital to Analog Converter Box(CM7003) there is an RF out port and an RF in port. If you scanned channels with the cable in the RF out port you will not scan anything. Connect your cable to the RF in port and rescan the channels.
If you checked the cable and you have the right port connected then please verify that your cable is connected to a TV antenna or Unencrypted Clear QAM. If you are not sure, please contact your cable provider or follow the cable to see if it is indeed connected to the antenna. Remember, the Digital to Analog Converter Box will not work with Satellite or Cable. It will only work with Antenna, or Unencrypted Clear QAM.
If you are still unable to scan channels please contact channel support for further help to resolve the issue.