If you suddenly have issues hosting...

[BlitzPig_EL]

Like inability of players to connect to your server (hosted from your own computer), check to be sure that your Windows Firewall has not been turned on or in other ways changed.  It happened to me.  The latest Windows update turned it and wiped several exceptions that I had placed in it some time ago.  All returned to normal when I disabled Windows firewall. (I run a stand alone hardware firewall in my router).

 

Just a little heads up.