I had a problem with no sound in Minecraft. It was very hard for me to find the solution on the internet, so I will post how I did here. This might work for you if your game crashes when you try to enable sound in game.
2. Go to Minecraft folder, press Start > Run and type in %appdata%/.minecraft/
3. Open bin > natives and delete the OpenAL32.dll file, also delete the other OpenAL64.dll (i think) file, just to be sure.
4. Go to C:/Windows/System32 and copy the OpenAL32.dll from System32 folder to %appdata%/.minecraft/bin/natives/
5. Now you have replaced the Minecraft OpenAL32.dll with the new OpenAL32.dll, open Minecraft and go to options and enable sound. This should work now. :-)