Please email aj at signalhound dot com and I can help you further. Please send me the following information.
1) What is the S/N of the unit?
2) Did you buy the unit new from us? How recent?
3) If the front end is damaged (such as a switch/atten) you may not see a signal. Is it possible the unit was damaged due to static or high input (> 20dB). Are you grounded when attaching your antennas?
I look forward to your response.
Andrew