I also cannot host games. Via steam, when I invite friends they receive the message 'Server is not responding.' I get the same when I try to join their games. As for multiplayer I can join matches online with no trouble and little to no lag. My server admin buddy was trying to figure it out and he believes it's nothing to do with port routing or firewalls, which is what I first suspected (Like the OP, I'm also not computer savvy). Hopefully there's good info on this somewhere or soon will be.