I have had this problem before.
Mine would sit at "wait for host" and once in a while it would actually join a server. It was about 2 out of 30 tries that it would actually join a server.
Worse yet.It required a reboot of my pc to get out of the "wait for host"
I also tried everything from reinstalling several times,removing all registry settings,mucking with all network settings,opening various ports,tried different network adapter even. I also have no firewall or virus software that runs so I know its not that.
I also have played Arma on 4 different PC's that I have and none of them ever did it.When this was happeneing I just used my laptop that didn't have the problem.
Since I reformatted and reinstalled it no longer does it and I still do not know what was causing it.
I think it was some piece of software I had installed before.
I am very good at PC's and I was stumped.Thankfully my new PC doesn't have the problem.Was my last PC that had the problem till I reformatted it.
Good luck and sorry I am not much help