If you have onboard sound via a Realtek sound chip, there was a driver conflict with a very recent Windows Update on Windows XP. You may want to try updating your sound card drivers. Realtek provides drivers directly that work with the vast majority of onboard sound cards based on their chips.
If that doesn't work, please describe the issues your having in much more detail. Exactly what is happening and what steps you can do (click here, do this, type step-by-step) to reproduce them.