There are a few things you can do to troubleshoot and fix a surveillance system that is down:

1. Check the power: Make sure that all of the cameras, the recorder, and any other components of the system are properly plugged in and receiving power.
2. Check the connections: Make sure that all of the cables and connections between the cameras and the recorder are secure and not damaged.
3. Check the software: Log in to the recorder and make sure that the software is running properly and that there are no error messages or alerts.
4. Check the network: Make sure that the recorder is connected to the network and that it has a valid IP address. If you are using a wired network, make sure that the cables are plugged in and that the network switch is on. If you are using a wireless network, make sure that the wireless access point is turned on and that the recorder is within range.
5. Check the cameras: Make sure that all of the cameras are turned on and that they are properly positioned and aimed.
6. Check the recorder: Make sure that the recorder is not full and that there is enough free disk space.
7. Check the resolution: Make sure that the resolution of the cameras are supported by the recorder and the network bandwidth.
8. Check with manufacturer: If the above steps don’t resolve the issue, try contacting the manufacturer of the system for further assistance or check the manufacturer’s website for troubleshooting tips and advice.

It’s important to keep in mind that some issues may be resolved quickly, whereas others may require more time to diagnose and fix. Depending on the complexity and size of the system it may be helpful to get a professional help.