Well, for the people who are experiencing the same problem, these are the symptoms:
Singleplayer starts normally.
Freezes at Splash Screen.
No errors.
Splash Screen gets a frame at the bottom and to the left, no other side.
Veryfying with Steam wont help.
Have to shut it down using the Task Manager och by clicking on the Splash and then "Close program" when the window of options pops up.
I actually figured this out before, but I was too busy playing the game I forgot to post. The corrupt file was "mp_playlists_dlc1.ff" in "Steam\steamapps\common\call of duty modern warfare 2\zone\english". Delete it and you should be able to play again.
I have also heard about the "mp_playlists.ff" being corrupt (udin39 also said it). But deleting this was not the solution.
Thanks for your help anyways
