Plex Server not connecting since an hour, how to fix ?

Dont know, whats wrong, server is online and everything is fine, but still Plex doesnt connect.

Im getting error screen.

What to do ?
How to find out what happened ?

I have 7TB of movies, dont want to lose my library, please help!!!

Start with restart of your machine. Make sure the PMS is running and then go to http://ip_of_your_pms:32400/web
Meanwhile you can also provide logs.