i just got left 4 dead 2 from my friend and guest what i can only run the multiplayer mode. it worked perfectly fine on my friends computer.

If it successfully installed to your computer and you can play part of it but not all, I'm guessing it's a driver issue. Go to your computer's manufacturer's website and run a system driver update. Also something I always bring up when giving computer advice is be sure to faithfully run disk clean-ups and de-frags. Not doing so can affect performance in many different ways.

Validate the game files from Steam and if necessary download all of the updates for the game as well. Valve is always releasing updates, especially for the new OS, so if it doesn't run initially chances are it needs to be updated to work. Also make sure you have the correct DirectX installed or you may run into compatibility issues.

thanks for the quick reply. i think i left out something. oh ya, the game did not need to be installed. i just extracted the files on the disk and it could already run but just the multiplayer part.

steam has to let you get on the multilayer.