I put a DVD in the computer, but there's no sound.
If you put the DVD in the computer and it automatically started in a program called Real Player, exit out of Real Player completely. The DVD needs to be viewed using Windows Media Player. To find this program, go to the Start menu, and type "Windows Media Player" in the search box. Once in Windows Media Player, find the DVD in the left side menu and click on it, which will then display a menu with all the chapters in the DVD - click on any chapter to start watching the DVD.
If this fails, try another computer; the problem may be the computer speakers themselves.