First of, is it onboard sound or a pci sound card?
If it's onboard sound then goto msi's website, then goto there download page for drivers & then type in your motherboards model number. That should sort you out.
If it's a pci sound card & there is no obvious markings then look at the chipset on the card. It's the little numbers or letters on the black chip & do a general net search for them.
Might look like: AD1897
www.driverguide.com is a great site for downloading any drivers.
Hope that helps.