Steam won’t launch left4dead. Windows has no issue launching it, the only issueis that if i start l4d2 from C:\Program Files (x86)\Steam\steamapps\common\Left 4 Dead 2, eventho the steam is running, when l4d2 finally runs, it apeas with a VAC- insecure starting screen and it doesn´t let me get in to co-op.

Already try with verifying the integrity of the game files as well.

Any advice helps.