Iphone 5 lightning cable not working and phone is dead what should i do?

It said in my iphone 5 that the cable wasn't authorized and my iphone is dead and the cable isn't authorized i need help

Buy a new cable or take it to the Apple store, where they will tell you to buy a new cable.

You can:
Take it to either bestbuy or Apple's geniuses to see what the problem is

or you can buy a new cable