There may be a fuse in your amp that has gone. The fuse, in the harmonica player in my band's Fender Bassman, went about a year ago. She didn't have a spare, so decided to wrap it in silver foil, fit it back in the amp, and carry on. It worked, but it could have caused internal damage to the amp (and her) if there was an electrical issue with the amp, which caused the fuse to blow in the first place.
She now carries spare fuses to every gig.