Make sure you have updated to the latest firmware version, the old firmware is very buggy. I have an issue with a K4 where in it will get a stuck button, when this happens the other 2 K4's in the system wont work, the only way to stop it is to power cycle the CB-4. Try this--> create a new system file that only has a video viewer on the home page of each of the K4's nothing else, If you get a picture on both then add 1 button that toggles between two inputs, if that works add 2 buttons each of which selects a different input on the elan. if this works, you for almost certain have a coupt page in your original file, you will need to erase that page and start over. Dont even bother doing any of this unless you have updated the firmware first.