It's probably the amp, do a search here on the site and you'll see that amp failure is somewhat common. Per your description of the problem everything works but you have no sound, well what makes sound... the amplifier.

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2002 X5 4.6is
1999 C5 Corvette
1992 Mitsubishi 3000GT VR-4
1994 Kawasaki ZX-9R
2005 Mazda 6 Wagon (Wife's)
1991 Mitsubishi 3000GT VR-4