Greetings mikespence127,
Welcome to the Apple Support Communities!
I understand that you are unable to sign in to FaceTime on your Mac. In this situation, there are two different articles with troubleshooting information that I would suggest reading over and working through. If the issue continues, please let me know the exact error message you receive when trying to sign in to FaceTime on your Mac along with any other additional information you think may be relevant.
FaceTime for Mac: Troubleshooting FaceTime - Apple Support
Get help signing in to FaceTime, Game Center, Messages - Apple Support
Cheers,
Joe