It is absolutely not powering up when you hit the button? If so, I"d try disconnectoing the battery (again, I Know) for about a minute and reconnecting it. Then try turning the radio on again. Also, look for a blown fuse in the fuse panel on the driver's side under the hood. Beware there are several fuses related to the radio - check all of them.

Or is is powering up and displaying "CHRYSLER"? This sounds like the "lock code" mentioned above. I'm totally ignorant of how to deal with this, with two cars and five years of ownership, I've never dealt with it.