First check the device manager to ensure that the sound card is not loaded properly - ? or red x.
If not determine the the type of sound card (open the computer and look) - delete the card from device manager and on restart see if the system will tell you the type.
Then, do a search on the internet for the sound card driver.
Download the driver, install the driver. - If needed, remove the device from device manager and restart - pointing the system do the location of the installed driver.
(with luck windows will find it on its own).