First, check your speakers or headphones. There are cases when waste contact or simply the cat chews through the wires. Connect them to any audio device with a suitable connector, whether player or cell phone, and check the sound. If in this case it is not, then, most likely, the speakers will have to send either in for repair, or in the trash.
Second, check for updated drivers for your sound card. To do this, right-click the mouse on the icon "My computer" - Properties – Hardware – device Manager. If the icons of the audio devices are yellow exclamation marks, then go to properties and follow the instructions to reinstall the driver. If the device Manager does not display the damage, open control Panel – Sounds and audio devices and look for device input/output. If they are not displayed, install the driver manually from disk or download from the Internet. Model sound card you can also see in device Manager.
If earlier the sound was working, but suddenly disappeared, then you may have a virus on the world wide web and he must as soon as possible to get rid of. Download Kaspersky Internet Security 2012 from official website, install on your PC and activate the trial version for 30 days. Configure the antivirus scanner to fit your needs and run a full system scan.
Often sound problems are resolved by a simple reinstall audio and video codecs. Most popular and free collection of codecs is K-Lite Codec Pack. Download the updated version and install over the old one. If you just connect to the Internet on a new computer or operating system, it needs to be done first, because without codecs no sound or video will not work properly.
But if the sound is heard only when working in the browser, update your Flash Player or install it if it hasn't been done before. Most Internet players are working on Flash technology and no player not functioning. Please note that various programs to edit audio files or the audio controls on the PC, which minimized to tray, can act uncontrolled in the network. So unplug them and check the sound. This files most often lack a standard mixer from Microsoft, other programs only load the system.