there is no sound output on the speakers anymore

there is no sound output on the speakers anymore

I dont understand much of the internals of my technical devices, unfortunately. Its getting power and I can turn it on, LED's are shining from inside and from the power button. Also you can connect other devices t the AC-Power Outlet. But there is no sound output on the speakers anymore. I tried every input channel, different cables and every output speaker channel. All dead output.