My aftermarket radio won't turn on, neither will my old stock radio. What could be the problem?

The radio doesn't get power anymore. I've replaced all the fuses related to the radio (I
think) and I've tried changing harnesses for the aftermarket radio and still nothing. What
could be the problem? I've even tried putting the red wire to the yellow and still nothing.
The harness I used first was METRA 71-7550. Then I tried using the amp harness 70-
7551 and still nothing. The amp harness does bring the noise of the engine to the
speakers but still no power goes to the radio. I need some help.