Be sure to plug into the "green" socket on the front of the computer, not the "pink" (microphone) or "blue" (headphone output from iPod) socket.
Try the speakers in the "green" socket on the back of the computer, to ensure that the speakers work, and the volume control is "high", and that you have not "muted" your speakers.
Some motherboards have a small "jumper" to enable/disable the front audio-output sockets.
Try the speakers when connected to the headphone-output from your iPod, to confirm that they work -- they could be quite quiet.
Answers & Comments
Be sure to plug into the "green" socket on the front of the computer, not the "pink" (microphone) or "blue" (headphone output from iPod) socket.
Try the speakers in the "green" socket on the back of the computer, to ensure that the speakers work, and the volume control is "high", and that you have not "muted" your speakers.
Some motherboards have a small "jumper" to enable/disable the front audio-output sockets.
Try the speakers when connected to the headphone-output from your iPod, to confirm that they work -- they could be quite quiet.