Hey i was just installing days and when i read on wiki this:

Open Steam.
Click the Games menu.
Click Add a Non-Steam Game to My Library.
Click Browse.
Navigate to, most likely, C:\Program Files (x86)\Steam\steamapps\common\arma 2 operation arrowhead\Expansion\beta. If you are not running 64-bit Windows, remove (x86) from the path.
Choose arma2oa.exe.
Click Open.
Click Add Selected Programs.
Open your Steam Library.
Right-click arma2oa in your games list, and choose Properties.
Rename it from "arma2oa" to "DayZ".
Set the Target to: "C:\Program Files (x86)\Steam\steamapps\common\arma 2 operation arrowhead\Expansion\beta\arma2oa.exe" "-beta=Expansion\beta;Expansion\beta\Expansion" "-mod=C:\Program Files (x86)\Steam\steamapps\common\arma 2;Expansion;ca;@dayz" -nosplash If you had to modify the path in step 5, do so here as well.
Set the Start In line to: C:\Program Files (x86)\Steam\steamapps\common\operation arrowhead If you had to modify the path in step 5, do so here as well. <--- Here i stuffed up, Cuase i didnt read the last bit and i didnt have to modify the path in step 5. And now i forget the Code That i replaced with :

:\Program Files (x86)\Steam\steamapps\common\operation arrowhead


So if you guys could comment your start in Script, Please Do Check by going to:
Steam>Arma2oa.exe u added into steam n turned name to "Dayz">Right click then>Properties

WILL REP FOR 3 weeks If you Help ME