Cannot log-in to Messages app
I have a mid-2012 MacBook Pro running OS High Sierra version 10.13.1 - prior to a few months ago, I have never had any problems with my imessage account whatsoever. I cannot pinpoint the exact date (since my conversations have disappeared), but I believe it was sometime after downloading the first version OS High Sierra (late September) that my account stopped working. At first, I was not able to send messages, then I was logged out and I haven't been able to log in since. iMessage works fine on my iPhone 8, my apple ID is valid, the only problem is with my MacBook. When I try to log in, I get this notification:
When on the Messages preferences page, this is what I see:
This page is static, and when I try to put in my information I get this notification:
I have already tried everything on this page without any luck: If you can't sign in to your iMessage account or FaceTime on your Mac - Apple Support
This issue is extremely inconvenient and I would really appreciate any insight into the problem.
Thanks.
MacBook Pro, macOS High Sierra (10.13.1)