Why does my stereo have power but no sound?
Check each set of wires and speakers to be sure no wire or lead is connected to a chassis ground. The radio will see this as a short and turn off the internal amplifier causing the on but no sound issue. Each speaker connected to the radio needs dedicated positive and negative leads from the radio to each speaker.
What are the signs of a blown speaker?
The most common aural indication of a blown speaker is an unpleasant buzzing or scratching sound, by itself or roughly at the pitch of the note the speaker is attempting to reproduce. Or there could be no sound at all.
What would cause a speaker to stop working?
Speakers eventually wear out. The rubber surround gets oxidized and cracks, voice coils come loose, or get fried when too much voltage goes into the speaker.