No panic my friend! Just repair yours windows installation using a bootable service pack disk/CD. This should cure it, before we think of reformating the hard-drive. Just sometimes, anti-viruses may not be exactly perfect; just like we humans. Also, let me ask you if you do have the right audio driver for your PC. Visit the website of your PC manufacturer to ensure you have the right driver for audio. If you can't find the audio driver for your system, I'll recommend you to install Windows Vista on your system.