There are many reasons why you possibly can't see your cameras.
1) The cameras are physically disconnected,
2) There is no internet
3) Changes in service providers
4) System may need firmare upgrade
5) Your monitor may be turned off.
6) You might need a step ladder.
7) Your TV source might be in something other than HDMI.
If you need assistance please call (562) 215- 4300 to speak to someone to further assist you.