If it’s Davis drives you have?
As it says in the thread I linked to:
[quote]First uninstall the old drivers. The download of the old drivers from Davis has an uninstall feature. If you deleted this you may have to go back to Davis and download this again.
Remember after installing the new drivers you have to do to Control Panel > Com Ports> click on Refresh list of comports and select the URART to USB selection.
Hugh