Make sure the speakers are plugged into the correct port on the back of the machine. You should see 3 different ports to plug in the speaker cable.  You will want to plug it into the port that shows an arrow pointing out of either a circle or half circle.  It will more than likely be the middle port. 

To test whether or not the speakers and sound card are now working:

1. Click the Start menu

2. Select Control Panel

3. Click on Sound, Speech, and Audio Devices, or if you're in Classic View, click on Sounds and Audio Devices

4. Click on Sounds and Audio Devices link

5. A properties window will open

6. Click the Volume tab if it isn't already selected

7. Verify that Mute is not checked

8. Click the Advanced button under Device volume

9. Verify that none of the options are Muted and the volume levels are set in the middle

10. Close out of the Volume Controls window

11. Click the Speaker Volume button under Speaker Settings

12. Verify that the speaker volume levels are set towards high

13. Click OK

14. Click the Sounds tab

15. Under Program Events at the bottom of the window, highlight a sound that has a sound icon next to it

16. Click the Play Sound button