I've used the CD key changer, tried doing it manually, tried everything. It still wont work, every time i go to log into multi it throws up the same "This key is not registered pleas use the cd key changer" type error, even after ive used the changer 10 times now to change the key it still doesn't work, running it as admin doesn't work, putting it into the ini file manually doesn't work, same error every time, i'm at my wits end here.

I'm on Win 8.1 if that matter, i didnt have this problem before my reformat though.

Not enough information. What game? What are you trying to do?

You'll want to post the exact error. I think everyone gets an error on mulitiplayer now b/c the Gamespy servers closed down. I'm not 100% sure, though. I haven't tried in a while.