Check your wiring on both Input and more importantly on the Output VERY CAREFULLY. Makes sure that the connections are clean, tight, and secure with no stray strands of wire potentially shorting the output. Make sure nothing has dropped behind the amp and shorted the output terminals. Same with the speakers, make sure no stray strand of wire or foreign object is shorting the wires at the speakers.
Next disconnect everything, and turn the amp on with nothing connected. Admittedly hard to tell, but does the amp seem to act normally.
Next, with the Amp OFF, connect the speakers are turn it back On. Does it seem normal.
Next connect the simplest most basic single input you have - turntable or CD Player - and turn the Amp ON, and see it everything looks right. It it does, try playing some music. Make sure you have the correct input selected. CD for CD, Phono for Phono, or whatever.
With only amp and speakers, try rotating the various dials and clicking various switches and see if you hear any sound. Switches can corrode, and rotating or switching them multiple times can sometimes wipe them clean.
Make sure the correct speakers are selected. Perhaps someone has turned Speaker-A off.
Really you have to go through a systematic procedure to determine exactly where the problem is. Perhaps you have blown a speaker, and that is shorting the output. There are a lot of possibilities, but a systematic and logical approach should help you narrow it down.