Re: no power to head unit?
did you check ALL the fuses? the fuse box under the hood too?
do you have a multimeter? if you do check your voltage to your yellow wire (constant power) that wire should have 12v when the car is completely off and than check your voltage to your red wire (switched power wire) it should have 12v when your key is turned on.. also make sure and check your ground (black wire) hold your negative off your multimeter on the black wire and the power side ofyour multimeter to either your red or yellow wire which ever has power.. if it says 12v it means you have a good ground.. if it reads nothing your ground is bad.
so what am i gonna do if i have a bad ground?
If you do happen to have a bad ground, just take your black ground wire from the back of the head unit and attach it to a good, clean spot of metal on the vehicle chassis.
how did you rewire the cd player? to ignition harness or fuse box?
Okay, as alexbuck205 said, if you have a multimeter (or worse case a test light) test both your +12v (yellow) and your ignition (red) wire on the back of the head unit. That will be the easiest way to diagnose your issue.
Always check fuses under the hood as well as inside the car. Sometimes the blown fuse will be labled something that seems like it wouldn't have anything to do with the radio.