Q: My facetime on my mac isnt working

Hello, the facetime on my mac isn't working anymore. It is not even showing the preferences for facetime again. I have tried logging in with my Icloud email but it keeps on saying the registering device does not have appropriate credentials. Please I really don't know what to do.

Thank you very much,

Neto

MacBook Pro Retina 13-inch Late 2012

Processor: 2.5 GHz Intel Core i5

Memory:8 GB 1600 MHz DDR3

OS X 10.8.5