05 Trailblazer Radio problem.

I was wondering if someone can help? I have a jl audio dvd/cd player in my trailblazer, it has worked fine. The other day it stoped working. I took it out to test it on the car battery and it worked fine. I put it back in and hooked all the harnesses up and put the power and ignition wires together and it worked. When I have everything hooked up right the radio will not work. All fuses are good. There is not 12v to the ign. wire when key is on (i tested that). Any ideas.