Do you have a server metamod installed (or any other game mods that mess with server/client DLLs?) - I was trying to help someone else debug their game with the same issue and he tried everything (including a reinstall) and it kept giving a CTD without error until he removed the server mods. If you don’t have any mods installed you should verify cache integrity and update to latest graphics drivers to see if that makes the game work.
If you have some way of debugging memory dumps (.mdmp files) then you can also examine those to pinpoint the source of the ‘crash’, it should be generating one in the base L4D2 directory every time the game crashes.