Soundless mystery

if the unit powers up and u can use it but not listen to the music then u dont have a security reset as that would restrict the unit from getting power (from my knowledge anway)  i found that most of the pioneer models i've installed have pretty much the same wiring harness (checked the website and they seem to keep the color coding the same for the different HU's)   the color coding is the same the speaker wires are purple, green, grey and white, if one of the speaker wires is grounding out the music will not play so make sure no wires are touching eachother or grounding out somewhere.  also there is a mute wire which i think is yellow with white stripe (not too sure as on some models that is the dimming wire for the HU light.) actually i just checked the website and the mute is a yellow with black stripe.  but if u have the mute wire hooked up or grounding out somewhere then it wont play but it would also be obvious as it would say -Mute: ON-  I'm not an audio pro, but i cant think of anything else other than a speaker wire possibly grounding unless the HU is shot.  where did u get the HU?