I have been playing COD MW2 successfully on my PC (Win 7) for several months now. Single player still works great. I have dual monitors running on two NVidia GeForce GTX 285's. Computer is working properly. I changed the resolution of COD MW2 multiplayer to windowed and a lower res than my monitor's full res (HD), then moved over to secondary display. Played fine. I exited the application (was done playing). Tried to get back into multiplayer and program crashed then went directly into debug. I am now stuck. Single player still plays fine. Steam still working fine. Other games still working fine, even on second monitor and even when running from steam. Any suggestions would be appreaciated. Do not know where startup config files are for COD MW2 MP.
Have you tried verifying the game cache? If not, please try to do so by visiting here: https://support.steampowered.com/kb_article.php?ref=2037-QEUH-3335. Once you have done so, try running the game once more. Also, you may want to consider uninstalling/reinstalling the game if verifying the game does no work. Be sure you restart your computer after each solution (Once after verifying, Once after the instal). Please let us know if any of these helped you out. ^JG