Well, at the most simple end, have you gone to Edit/Preferences/Audio Hardware and re-selected the proper mic input just in case the change of driver confused something.
Or, if it is a driver issue, perhaps you could download and try Asio4All from http://www.asio4all.com/ . That might let your system bypass the potentially faulty driver. You'll have to change settings in the Edit/Preferences/Audio Hardware menu to reflect the change of driver--you can also set up Asio4All from there.