First ensure you have connected the speakers to the green connection.
There are 2 possibilities.
You will always have a green connection grouped with all the others that run off the mother board.
If using the built in sound on the mother board you will need to ensure the on-board sound is enabled in the bios.
As the system boots up you will see a line of txt that will say; press F2 or delete to enter set-up.
Within the bios set-up you need to select the 'chipset configuration'. On the page you need to ensure the AC97 is enabled.
Save and exit. Do not alter any of the other settings!!!
Click, START then CONTROL PANEL. Select the SOUND & AUDIO icon. Make sure the Mute does not have a check against it, if so remove and apply.
You may also have a seperate sound card.
If this is the case the on-board sound in the bios needs to be disabled (as above).
Check within CONTROL PANEL, SYSTEM, HARDWARE and select audio devices ensure the drivers are installed for the card.
Hope this helps.
Would be better if I knew what software, motherboard etc you were using.
Les Jones, March 2008