do this
Start -> control panel -> Device Manager -> sound,video and game controllers
click on the sound,video and game controllers theres will be :
High definition Audio or Realtek High definition Audio
right click on it and Disable it > yes > yes > it will restart the pc or laptop
then when ur pc starts again it will popup a window asking u to solve the problem with the sound
just go through it and its done
thats work for me ( Alienware Laptop )