Suddenly, my sound device is not working properly. There is also no "speaker" icon on my taskbar. When I try to open any songs, there are some warning message "Cannot open the audio device", "The audio system files are missing or removed", and etc. When I open the movies, I can see only the pictures, but not sound. How can I solve the problem? Thank you for your help!

The best source for audio drivers is the computer manufacturers web site.

If the computer was custom built then go to the motherboard manufacturers web site.

Go to the driver download section and insert your model number. The drivers will be there.