Unless your computer has an HDMI port, it probably doesn't have integrated audio and video output. That means you'll have to use separate cables to get both video and audio working on your TV. If your computer does have an HDMI port then both audio and video will be transmitted though that single connection.
To hear the audio from your computer through your TV, you'll need to connect an audio cable from your TV to the audio-out or headphone jack on your computer. (If you have external speakers connected to your computer, you can also use those to listen to the audio.)
In most cases, an audio cable with a 1/8-inch stereo jack on one end and red and white RCA connectors on the other end is the simplest option. Computers with high-end audio cards may also have an optical audio or digital coaxial audio port. These higher-quality audio connections can connect to a 5.1-enabled stereo receiver for full surround sound, but they cannot connect directly into most TVs.
To optimize your computer's volume settings: Click and drag the volume indicator in the video player to increase or decrease the sound level. Also check the Main volume and Wave volume in your computer's operating system. To avoid sound distortion, steer clear of setting the volume above about 80% of the maximum volume on your computer. Also please make sure your computer's volume is not muted.
To optimize for 5.1 surround sound: If you're using an optical or digital coaxial connection for your audio connection, you may want to verify the settings on your computer to make sure you're set up for 5.1 surround sound. (Note that not all videos are available with surround sound.)
On a Windows PC, go to Control Panel and open Sounds and Audio Devices. On the Volume tab in the Speaker settings section click the Advanced button. On the Speakers tab, verify that your Speaker setup matches your speaker configuration. For example, if you have a six speaker 5.1 stereo system, select 5.1 surround sound speakers.
Note: if your Speaker setup is set to a mono setting, you should change the setting to an appropriate stereo setting as some videos encoded with 5.1 surround sound experience low center channel sound with a mono setting.