Welcome to the Apple Support Communities!
I understand you recently had an issue with your iPhone 6 where you were logged out of all apps, and now you can't activate iMessage. The resource below will help you with the iMessage activation issue:
If you get an error when trying to activate iMessage or FaceTime
However, there seems to be something much broader going on here. What app were you using when your iPhone stopped responding?
Do you have a backup of your iPhone 6 in place for situations like this?
How to back up your iPhone, iPad, and iPod touch
Did you recently update to the latest iOS operating system, or do you need to do that?
Update your iPhone, iPad, or iPod touch
Hannah, please reply to this thread with any additional information that you can, including any specific error messages that you encountered, and I'll do my best to help you.