start >right click my computer icon> chose properties > choose hardware tab > choose Device manager button.
While in device manager look for sound or audio and game controller and see if there is any x or !. If there is then you have probably lost the driver files or something...double click the line and read what the error says.
Repost the error.
go to the manufacturers website and look for driver downloads for your model of computer. Find the audio drivers and download to desktop. Close out all windows and double click the driver icon and the driver will install. Navigate back to the device manager and the audio adapter there and choose the driver tab. Then choose to uninstall the driver and follow the prompts to do so and reboot your computer. Upon reboot the found new hardware wizard will find the sound card and reinstall the new driver.
You should then have sound.