First of all, check the obvious: are the speakers in the correct outlets on your sound card, has sound been disabled, volume too low in the control panel and so on.
If not, go into the device manager (right click on my computer and choose properties).
In here see what there is in the line of sound devices and check if any of them have an exclaimation mark.
Remove the sound card from the device manager and reboot.
Get the latest drivers from the manufacturer site and see if you can install them.