Question on Fosgate 4100 no sound output

I use Fosgate 4100 amps with Metric Halo processors. I have 3x of them, (Fosgates) for different recording studios and theater environments.
The home theater 4100 started acting strange you would turn it on and power light comes on but no Sound -- then i would flick the power switch up and down 7x and eventually it would turn on the sound comes on.
I did this for a year and then it would go to 10 flips up and down and now it doesn't output anymore at all no sound -- i bought a new one on ebay
and made sure the guy guaranteed it and checked it before it left
he did and he said it sounded great i finally installed it and no sound output. I tried the same cables, power, input and speaker cables and everythign works so the amp is toast.Why?