Who can help me figure out why my radio doesn't turn on even though it's getting power? It happened with the last radio too. And the 12v constant wire is only getting 4v. And the fuse on the back of the radio doesn't get any voltage in general car being on or off. All the fuses have been checked and they are good.

There are 2 fuses to the radio, one is under hood and sounds like it is partially blown (constant). The other is labeled radio and should be inside (accessory). If you are only getting 4 volts on the constant it will not turn on.

Oh okay, but which fuse would it be under the hood?

Iirc its the dome sipervision. But I could be wrong. I am assuming you have a voltmeter. I would hook one lead to ground and check both sides of each fuse until you find the one giving you 4volts. It most likely will be a small fuse around 10 amps. Very rarely have I seen a maxifuse or fusible link go bad and just the radio stop