|Go to Windows Device Manager and see if there are any yellow or red exclamation marks there. |
While there, look for any listing for a sound device. If you see one then post back with what it says there.
If there are not any, then reboot the computer and continuously tap the Del key until the computer boots into the BIOS. Read the screens to learn how to move around in there. It will be keyboard only, no mouse. Look for a tab across the top that says integrated hardware. Highlight it by moving with the keyboard. Arrow keys, pg up/dn, enter, tab, esc are most of the key you need to use. Look for a sound device that may be set as disabled.
If your brother used an add in sound card he probably disabled the onboard sound device. Enable it and save when exiting by hitting F10.
When WinXP boots up you should then see a message that Windows has found new hardware. Hopefully it will automatically install it.
Post back with an update.