Sometimes there is a fuse inside of the CB; pop the cover and see.
Most CB's have a protection circuit against reverse hookup.
When/if you do pop the cover smell inside the CB and if you smell something burt, well...
When you hooked the CB up to the battery the second time:
1) Did you have the Microphone install when you tried to turned it on; I believe the Cobra's need the mic in place ?
2) Were there any lights on when you turned it on ?
3) I am going to say this but don't get pixxed, RED = 12V pwr, Black = Ground ?
Let the site know what you find when you open her up.