Cd key changes

Ok i have my real cd for arma2 implement or showing or entered or whatever before i start arma 2 oa but when i start the game and join a server i get cd in use... well my problem is that after i close the game and check wat my cd is the cd key has completely changed to a diffrent one and i need help to prevent this( no hacks are being used currently)

i think you opened arma 2 oa from steam and if u did that then open arma2oa from this directory C:\Program Files (x86)\Steam\SteamApps\common\Arma 2 Operation Arrowhead
and if its dayz ur playing then just go into dayzcommander and choose it not to open dayz with steam! i hope it helped u!