If the speaker wires are easy to get to you can disconnect them and connect to a speaker in your hand, then power up machine to see if you have sound. That will be easier than swapping speakers.
When you followed the speaker wires to the speaker did you see any pinched wires or insulation rubbed off? If a speaker wire is touching metal chassis then that will short out the sound. Also, where does the other end of the speaker wires connect - the source of the sound? There is a sound amp on the mpu board near the blue volume control, and the mpu connects to the motherboard. Do the speaker wires go to the motherboard?
Also, you can remove the mpu board from the machine and take a close look at the blue volume control. Sometimes they get mangled by someone turning them too hard past the stop position. If the volume control is broken it may seem to move correctly but not actually be making connection. Take a real close look at it, post a photo for us to see too.