Onboard sound is enable but still no sound

I enbabled my onboard audio card by going to BIOS but still, no sound. When I run the device manager (to see if anything changed) it found a new device which is an "Unknown device".

My pc is "HP Compaq dc7800 Small Form Factor PC".
Recently I changed my graphics card from Geforce 8400 GS to Geforce G210.
My OS is Windows XP.

Any solution? :(