The sound suddenly died out? There was a yellow exclamation mark on the Crystal WDM Audio Codec on the computer. If you click the exclamation mark, it said that the device dosen't work properly. So, what happen to your sound?
You can try to download the latest audio card driver for your computer, and install it.
Guide to install audio driver
1. Open Device Manager by clicking the Start button Picture of the Start button, clicking Control Panel, clicking System and Maintenance, and then clicking Device Manager. Administrator permission required If you are prompted for an administrator password or confirmation, type the password or provide confirmation.
2. In Device Manager, locate your sound card under Sound, video and game controllers, and then double-click the device name.
3. Click the Driver tab, and then click Update Driver.
Popular audio drivers