Static IP broken, server closed with members in it.

I was playing with my friends on my server when all of a sudden the server appears to crash. Everyone is kicked but the server doesn't display a "crashed" message like it usually does. Trying to reconnect displays a "Can't resolve hostname" error. So we use the Dynamic IP, and everything works fine until the server closes itself (not a crash, but what happens when you press the "Stop" button. I did not close it however.) With 4 players on the server. What's going on?