Madaji

So, yesterday, I bought the ArmA II + Operation Arrowhead add-on combination package, entitled "ArmA II: Combined Operations" on Steam in the hopes that I could play the Day Z modification. Upon installing the two, I tried to open each one, individually. When I open ArmA II, it will go as far as the BI image, and then it closes the program, leaving a message stating that a "Bad serial number given in Setup". I tried to open Operation Arrowhead, to see if it, too, was acting oddly. OA doesn't even open, and instead leaves a long error message that I did not write down. I decided that the easiest and most simple of actions would be to uninstall and reinstall each program. ArmA II just got done installing, and OA is at about 10%. I tried to reopen ArmA II, but the same problem keeps occurring. I will not install the program a third time, as that is most certainly not the issue here. I expect that when Operation Arrowhead is done installing again, the same problem will arise, leaving me deflated and in need of reassurance, but I do not wish for this predicament to be that incessant for that long. Rather, I would particularly enjoy some assistance from any individual(s) whom have been having the same problem. Thank you for any help you offer, and I hope to see you online soon enough.

When I open ArmA II, it brings up a message, immediately after the Bohemian Interactive image appears, stating that I have a "Bad serial number given in Setup". Why would Steam or BI give faulty/used keys? Just doesn't make any sense, and it's getting a little infuriating. I literally just spent my entire day downloading ArmA II and Operation Arrowhead, deleting them, and reinstalling them to see if that would fix the problem, but to no avail. Any help for this little issue?

Same exact thing happens to me. I can't even get onto the game, whether it be ArmA II, or Operation Arrowhead. Also, I'm on Windows 7.