Why doesn't my Messages app on my Macbook Air 11" work?

Why did my Messages app on my Macbook Air 11" stop working?

It stopped out of no where, I don't even know how it happened. It works if I log in with my other emails. But the email I want to use with my Messages doesn't want to work. I tried changing the password but still doesn't work. I hope you could help me!

Here are a few screenshots I took.