For some reason my ATGM will not fire. I am getting laser lock with the guns and Muti-Rockets. But when I switch to ATGM, monitor will show distance and "TA", but I get no "C" on the monitor allowing me to fire. All buttons are as instructed: laser stand-by, Grd. Targets, (Enter) until it locks, box is locked on, but still nada. What could be the problem?