Plutonium

Hey guys,
I am new to this and I encountered a problem. I downloaded everything needed for mw3 and I set the designation in the IW5 launcher for MW3 in my MW3 folder in steam. When I tried to launch it, it gave me an error and closed immediately. I did not get a chance to see what the problem was. I tried to relaunch the game from steam but it does not open. Any help?