Cd player wont come on - Kenwood KDC-X590 CD Player

You need to first check a few things:

1. make sure the detachable face is securely on the unit.
2. make sure you have 12volts on the constant wire (yellow) and 12 volts on the switched accessory wire (red).
3. make sure that you're well grounded to chassis metal or the ground wire in the radio plug.
4. Lastly, there should be a 10 amp fuse on the back of the radio...check to see that it isn't blown.

If you find a problem with the power on the unit, then check your vehicle's fuse box.

You failed to mention what kind of car this is in. Some vehicles (Nissan, Mazda, etc.) have no ground wire present in their radio plugs.