Drivertest comes with the Mach install. Did you have Mach running when you double clicked on it, if so close Mach and try again. If it still doesnt work try a reinstall of Mach over the top of itself. Just make sure you have your xml backed up in the unlikely event something goes wrong.
Dont know what its like in Dundee but its still dark, a bit of snow lying and minus 3 Deg C in Carnoustie.
Hood