Aragon 4004 power light on but no sound

Hi all,

I have Aragon 4004 power amp that has an issue: It used to work well, however i just turned the amp off and in 10 seconds I turned it on again then I found it provided no sound. The power light is still on now. The aragon preamp has been tested, working well.

Does Anyone have any experiences and ideas? I appreciate your time reading this.