You need  to install the correct drivers for your audio adapter.

Just out of curiosity, did your friend give you any CDs along with the computer?
The drivers for your hardware devices might be on one of those CDs. If you
didn't receive any CDs, you might want to check with your friend. It will save
you a lot of time and trouble.

After installing XP, it's not unusual for some hardware devices to not work
properly. Go back to Control Panel and click on "Switch to Classic View" in the
left hand column. In the right hand pane, you should now see a System icon.
Double click on it to open System Properties. Click on the Hardware tab. On the
Hardware page, hit the Device Manager button. Note the items that have yellow
exclamation points or red Xs next to them. The XP setup routine did not have the
correct drivers for those hardware devices.

To fix this problem, you need to go to the computer manufacturer's web site and
download the latest drivers for your audio adapter. If your speakers plug into
an add-on card, you'll need to go to the web site of the sound card's
manufacturer to obtain the correct drivers.

While you're at it you should download and install drivers for your
motherboard's chipset along with any of the problem devices identified in Device
Manager.

If you're not sure what to do, post back with the make and model number of your
computer.

Good luck

Nepatsfan