This just happened while i was browsing the internet. The screen blacked out and came back on. After coming back on, the graphics card audio device was lost. Ie the intel display audio under the sound video and game controllers within device manager as well as the sound device under playback options.
Workaround is to restart.. however the device did get picked up again once when i added a bluetooth headset again.
Could you please let us know the driver version you are running? Please go to Device Manger> Display adapters> Intel(R) HD Graphics right click on Properties and then go to Driver, you will be able to see the version installed.