Just wait a short while. Sometimes nobody feels like hosting a working server. It's nothing wrong with your connection.

Also, servers that are grayed out are from a different version than yours. 1.23 can't join 1.24 (TSF) servers and vice versa. However, there is a program (Project Controller 4) that is able to trick your version of JJ2 into thinking it's a different version, thus allowing you to join servers of a different version. However, be careful, as joining a 1.24 server using 1.23 will crash if the server loads a 1.24-only level.