I have WLNB but can't record 4 channels at the same time

This will usually be a result of loose cables, so try reconnecting them and ensuring they are tightly screwed in, then reboot the box.  This should clear the issue.

Please note that if you want to record 4 things at the same time, you are not able to be watching a 5th programme at the same time. See Recordings troubleshooting for a full list of the different setups and how many recordings you can make simultaneously.