question monitor drivers

I have a Viewsonic Ultrabrite A90f+ monitor. When I installed Vista the only driver it could find was generic pnp driver, I downloaded the most up to date driver from the manufacturer, however it does not show. Although my ATI Catalyst says the drivers are installed. Now somehow the generic driver has been unistalled so that there is no way to change the refresh rate, which is grayed out at 60 hz.
Does anyone know how I can reinstall a driver for my monitor? I cannot click anything in Display settings that will let me, or in device manager.