Hello,
Which version of MW2 are you trying to play, the original 2009 release? or the newer reboot?
You mentioned turning off compatibility mode for the game and Steam but I want to double check if you did that directly on the main exe file inside your steamapps folder or if you just did it on the desktop shortcuts. Windows sometimes ignores changes if you only modify the shortcut.
Let me know exactly which files you right clicked on so we can figure out what is forcing that old OS version flag to trigger.