My guns will not fire at all

The most common reason for this is that the target is out of range for those guns. Check your radio log and you may see a message from the gunline stating that they cannot engage that target. You will need to move the gunline in order for them to engage this target.
It is possible that your radio messages are not being received by the gunline that you believe you are sending them to. If you use a callsign that is not used by this gunline, they will ignore the radio transmission. Check your radio log, if you are receiving replies to your radio transmission then you know your signals are getting through, otherwise check that no firewall is blocking transmission on the VBS3Fires ports. If this doesn’t work contact the support email address.
It is possible that your guns are out of ammunition. Check that you have given the guns the correct ammunition in the VBS3 editor, and that you have not already fired that many rounds during the scenario.