Hi Do you mean that you don't have sound on your system ?
Please do ensure that the speaker is receiving power,
If you do have another set of speakers please check with those speakers.
If both speakers do not work.
Please check to see the volume control is un-muted, If it is un-muted
You may check to see if the sound drivers are properly installed, This could be done in your device manager
1. Right Click on My Computer Icon
2. Choose the option Manage
3. Choose device manager
4. Select Audio/Sound Driver
5. Re-Install Driver
If that does not fix the issue, you could also run the Microsoft automated troubleshooting program and fix the issue too,
here is the link for it,
http://windows.microsoft.com/en-us/windows-vista/Tips-for-fixing-common-sound-problems
Use the Fixit tool on it, and it will do all the troubleshooting for you and perform the repairs if necessary,