i presume ur usb comes together with your motherboard and not and external usb card? and u are using windows xp?
then in such a case, go to the device manager. u can find it by typing this in ur run command: devmgmt.msc
nxt, check for any hardware in the device manager for any yellow question marks. for those with the signs, right click on the hardware icon and select properties.
under the driver tab, click update driver. you should see the hardware update wizard. when asked whether to connect to windows update, select no and then next.
now insert the driver cd that comes together with your motherboard and select the option intall the software automatically. click next.
now ur problem should be solved.. if not, reply again..