You have probably wiped the driver when you restored XP. You must go into the website of the sound card manufacturer, look in "support" and download the latest driver. Alternatively, find the driver from the CD / Floppy disk that came with the computer (if it was specially built for you by a computer store)
I have found that I can play music using real player but if I go into you tube the clips do not sound. Also no sound after booting up XP or closing down.
Check if the sound driver has been installed in the device manager?
1. Click Start, click Control Panel, click Performance and Maintenance, and then click System.
2. On the Hardware tab, click Device Manager. Double-click the type of device you want to change.
If you find an yellow exclaimation mark in the sound, video and game controller section, you will need to download the relevant audio driver from the motherboard manufacturer as previously stated.