Barthise

Ok, so recently I purchased Arma 2 on Steam and later purchased the Arma 2 Reinforcements pack from a local store. It shows that both are properly installed and up to date, but when I run the regular Arma 2 game from steam, it doesn't pull up the Reinforcements pack. On the other hand, though, when I start up the Reinforcement exe to play, it show's that the original Arma 2 is there and is playable with all of the original missions. My main issue is, I'm trying to play the DayZ mod, but my guess is that the Arma 2 on steam isn't recognizing the Reinforcement pack or the DayZ mod. I've actually tried about 10 different things and searched multiple forums/watched multiple updated videos on youtube, but have had no resolution with this issue yet. Any suggestions on what else I can do or try to fix it?