When you say it was 'worked on,' do you know what they did to it?
Go to start-->control panel-->system-->hardware tab-->device manager-->any yellow ! in there? If yes, and it's on your audio device, you need to install your motherboard audio driver.
If that's not the issue, open the control panel-->your audio manager-->make sure you have your type of speakers (2:1, 5:1..etc) picked for the audio output.