Editing your incorrectly can cause serious problems that may require you to reinstall your operating system.

First try to do a system restore. Here you can find additional information

If you can't do a system restore try reinstall your drivers for your sound card and see if the problem is solved. If not, try to repair your Windows and then reinstall your sound drivers. You can find information on how to repair Windows XP here.

If you can't solve your problem you should reinstall your operating system. Go here to learn how to install Windows XP.