MW2 PC only play

Is there a way to load the game on a PC and play without using steam? I bought a used copy and steam won't activate the key code. I don't really care about playing online that much. If I could just get it to work like a PS3 or Xbox does, I'd be happy.

If steam won't activate the code it means that it was already used. Not sure what other way would be feasible considering most games nowadays can only be installed one at a time (reduces likelihood of piracy).

If that's the case why are there so many used copies for sale?