check all of the fuses. You'll need to open it up and find the fuses that are installed on the driver board. I've had this issue with one of my B&K amps and it turned out I had a blown fuse on the driver board.
in the process, you may want to go to B&K's website and download their fuse spec sheet (I think it's in their FAQ section), and make sure all of the fuses are properly installed (ie noone replaced them with off-spec fuses)
in the process, you may want to go to B&K's website and download their fuse spec sheet (I think it's in their FAQ section), and make sure all of the fuses are properly installed (ie noone replaced them with off-spec fuses)