Have you downloaded the windows xp service pack 3? Try that first, then let windows find updated drivers for your usb ports if your lan connection is working. Use the options in windows device manager for driver updates.
SO it did recognize the USB devices at one time? What changed? I assume this condition exists with all the USB slots and multiple USB devices, ( i.e. the same USB key drive not working in all USB slots may indicate a problem with the device not the USB slots, for example )
Under device manager / Universal serial bus controllers, what is the state of the installed controllers/hubs? Any yellow exclaimation marks?