I have had this problem for several months now. Every time I turn my laptop off, I have to reinstall the audio device. It works fine until I turn it off again.
To re-install audio
Open Add Hardware Wizard in Control Panel.
Click Next, and wait for Windows to search for Plug and Play devices.
Click Yes, I have already connected Hardware.
Click Add a new hardware device,(at very bottom) and then click Next.
Click Install the hardware that I manually select from a list, and then click Next.
In the Common hardware types list, click Sound, video and game controllers, and then click Next.
In the Manufacturers list, click Standard system devices.
In the Models list, click Media Control Devices.
Click Next, click Next again, and then click Finish.
I finally went to the HP (my laptop is HP) troubleshooting tab and did everything they told me 3 times. Finally something must have worked since it has been fine the last 2 weeks. I'm keeping my fingers crossed. Good luck