It says "Server stopped." in the bottom left corner. Check the Settings button next to it, see if there's any errors listed there.
Ah okay I think I got it.
It gave that error when I tried opening my server and it said that the server wasn't running by default. So I pressed the start button next to and it said the server was running, and woo! It's working now.
I'll reply to this again if I encounter another error, but thanks for the help! You got my attention towards the solution, so that's great :D