My C: drive reently crashed. However, all my games were installed on my D: drive. The D: drive is a completely seperate drive and is just fine. I purchased a new C: drive and it's up and running now. Steam is up and running back on the D: drive and other Steam games work just fine.
Left 4 Dead 2 loads, plays the cinematics and then it hits the menu screen. It gives me a message that I have "-insecure" as an option and wont be on official Steam Servers. It comes to the menu screen and there is a message about Steam cloud but I can read it and everything is frozen at that point.