MAC Support-FACETIME

FaceTime has been working like a champ for the past 2 years. All of a sudden, when I click on FaceTime icon on my Mac OS X, it comes up perfect. When I select any contact, or when a contact calls in, our MAC automatically END's the call. we can FT between our IPhone's in the house, but not using the computer to our phones or vice versa. I've made sure all devices have all current softwares downloaded. I've read people reinstalling FT on their MAC, but still people said that it didn't fix the working of FaceTime. Anyone have steps on what to do at all???

I'm not computer savvy whatsoever, so you'll have to explain it like basics.