First thing is to check in the bios to make sure the onboard sound is enabled.
To enter the bios you must
press a key (such as F2, F12, DEL, ESC) or a key combination immediately after you turn on your computer(or you can restart it) but before windows loads.
If you are quick,you can see what button to press to enter set up when the pc is booting up.
If not just tap a key a few times whilst booting.
Onboard sound should be something like ac 97 audio or similar.