Hi,It might just be that you need to re-install your sound card drivers.
also check in your Bios that onboard sound is enabled.
Hi,If your onboard audio chip has died then the soltion would be to buy a Pci sound card,you can pick up a Creative card quite cheap nowdays and you will realy tell the diffrence in sound quality over your old intergrated sound
This one would do you fine,assuming you have a spare PCI SLOT?
http://www.newegg.com/Product/Product.aspx?Item=N82E16829102002