Everything should trace back to the factory fuseblock under the dashboard on the driver's side.
How did you handle the wiring for this head unit? Did you use an aftermarket harness to interface with teh factory head unit harness, or did you cut all the wires?
Step one is to throw the factory head back in there...just plug it in and see if it works - if it does, then you know that it's down stream of the harness, and there's a problem with either your aftermarket headunit, or your wiring job.
If the factory head doesn't work, now you can start by using a multimeter or a test light to check that accessory line. I would also replace the fuse if it looks good or not. sometimes they go bad, but still look ok....
There are a few other options on what to do, but those are the first two steps in trouble shooting this.
If the line is dead as it comes into the factory fuseblock, then you have another problem...