1. If using onboard sound, it must be enabled in the BIOS. If NOT using onboard, make sure the onboard sound is disabled in the BIOS.
2. Ensure your drivers are up to date, especially your main chipset driver for your motherboard. See the motherboard website.
3. Remove any old audio drivers if you have them.
4. Install the new drivers for your audio card or chipset. Make sure they are the newest AND for your version of Windows.
If you still have problems, hook something else up to your speakers to make sure they work.