Car Stereos: No sound from aftermarket stereo installation, chev trailblazer, speaker wiring

Question
I have a 2005 Chev Trailblazer. I installed a Planet Audio unit with a wiring harness the I bought. I made sure to match up the power and speaker wiring. The unit powers on and I get a display and it will play a CD but I get absolutely no sound from the speakers no matter which mode I switch the unit to. Any answers? Thanks.  

Answer
Keith, 9 times out of 10, there has been a short made during installation and it has caused the radio's internal amp to be shorted out.  The radio will need to be removed and bench tested somewhere to determine if it is still in working order.  Hope this helps, Scott