Start off with the basics.
Check the speakers actually work.
Make sure the sound volume isn't set to 0, or set to mute.
Make sure the speakers are plugged into the correct ports.
Does Windows actually 'see' the sound card in the device manager, and if so, does it say if the driver for it is installed and working correctly.
Try uninstalling and re-installing the sound card.
If it's an add-in card rather than onboard, re-seat the card.