MW2 KEY HELP Reeally NEEDED

Can Anyone tell me where i have to type in the serial that i got for my mw2 just got it and i cant type it in to steam so where do i have to type it in help me!!!!

why cant u type it into the steam?

Because it says that the key is wrong and my standts om dvd case and its not for steam SO HELP

same if its not for steam it should be working since it is a steam game. if it is not working, it mean that someone stoled the key at the shop, or that the one who sold you the cd-key is a scammer.

also be sure to don,t right a o as a 0 or 0 as a o and a B as a 8.... or i and 1.