You say you had a virus on your laptop, has it been removed? Do you know what virus/trojan it was and what damage it does to your computer?

My own recommendation, is after you have got rid of the virus, you should back up any files you don't want deleted and wipe your hard drive. Reinstall windows and reinstall the rest of programs you need, and drivers. It's possible that the virus damaged the sound card driver, which is why it is failing right now.

If you haven't got rid of the virus, life is a lot tougher for you. Cleaning one up is very tough, and usually requires much effort and special software on the part of the user. If you don't have anything important on your hard drive, wiping it and starting anew might be advisable anyway. If you don't want to do that, the first step is to download and run McAfee stinger. You may need to run this several times to destroy the virus.

Post back here if you need more info or help, or if this works. Or NDN could be right and you unintentionally messed with those settings.