I'm sorry but I don't quite understand what the problem is...
1) Do you mean the USB ports on your computer don't work?
2) Your USB modem doesn't work?
If number 1, then does any other USB devices work, such as a USB printer, memory stick, USB mouse, etc? Does the port controllers show up normally in Windows Device Manager? Are they USB 1.1 ports or 2.0? If your using ports on the front of your computer, are they hooked up inside to the motherboard headers?
If number 2, then did anything happen at all when you plugged your modem in? Did you install the modem drivers properly? Does the Device Manager show an Unknown Device (or another error) when you plug the modem in? Does any lights come on on the modem when you plug it in?
Or 3...I totally misunderstood the problem you are having and am chasing geese up trees.