xp doesn't recognize PL2303 Usb-serial Cable driver, why??

hi. when i first install the usb-serial cable, the drive works for xp and vista. It works in the first installation

today, i unplug the usb-serial cable for some reason and re-plug in it and it said doesn't recognize the driver.

i check hardware manager and i find it's "unknown device".

i try to reinstall the driver in many different ways, but it just doesn't work for my laptop.

i need it to connect to router console.

the only possible way to fix it for me is to format the computer and do the first installation
but that's NOT a technician should do. the cable comes with driver. i also download different one on the web. but it's basically the same. the driver name is "PL2303 USB-Serial Driver"

i also try it in other PC and it's the same(unknown device).

do you have any suggestion?

if i fix can it, i will NEVER unplug it again. >.<