usb storage driver missing

I no longer can use my external driver or any storage media including IPOD on
my computer. It comes up as unknown device and the driver is missing. I can
use them on another computer and the driver comes up as
windows\system32\drivers]USBTOR.sys I no longer have that on my computer. I
don't know if something happened to it or corrupted it. Can anyone tell me
where I can download a new driver or how to fix it. All the other components
such as my palm synch work.