You are probably connecting to out of date servers or you, yourself, are not fully up to date.
If you are up to date on all patches, open your server filter and under server name type "1.7.1.5" then under game mode (I think it is) type "DayZ" and hit "OK."
I've already been using this method. 95% of servers still won't let me connect. I managed to get into ONE working server over a three hour period, and about four minutes in it got hit by a mass-teleporting hacker. Fuck this day.