When you say the headphones work fine but the speakers do not, are you trying them from the same jack, or from separate jacks? My motherboard has the jacks for the mic and for the speakers reversed for some odd reason, you may want to try swapping.

Might sound like a silly comment, but make sure that any required power source (AC, battery) is hooked up correctly, and your batteries aren't dead or inserted incorrectly.

Can you test the speakers in something else, such as a portable CD player or iPod, or in another computer? It is possible that a wire became damaged during the system swap....

Brian.