My sony 771 won t play any sound -- not the speakers because doesn't come through headphones either. Just cleaned the lens for CDs last night, then this problem developed. Can see the amp bars moving, so what oculd be wrong?

The lit indication ("amp bars") proves that the aduio signal is getting through the unit's circuitry @ least to that point; lack of sound @ the spkr & headphones indicates the amplifier portion of the circuitry is either inoperative or disconnected from the load (i.e., either the speakers, or the headphones). A common cause of this type of problem cropping up unexpectedly is the headphone jack itself; in most products of this type, the audio path from the amplifier output to the speaker connection runs through the headphone jack, so the the speakers may be "turned off" when the headphones' plug is inserted into the jack. If the unit's owner uses headphones regularly, the most common problem to be found with the jack is loose solder connections to the printed circuit board's traces from the jacks' lead(s); in units with this problem whose owner's irregularly use the headphones, it's more common to find oxidization of the electrical contacts within the jack itself.