If your computer came with a motherboard disc the sound drivers could be on it click start control panel administrive tools computer management device manager scroll to sound,video and game controllers you might see a yellow question mark? Right click to reinstall drivers Click start control panel administrive tools computer management device manager scroll to display adapters + to expand you might see a yellow question mark ? or exclamation mark ! or a red x right click select reinstall drivers also you might uninstall restart your computer then reinstall the graphics card and its drivers

hope this helps