Cintiq 12WX black screen

I got my fiancée's Cintiq 12WX out of the loft today as we've recently cleared enough desk space for her to be able to use it. When I connected it it was seen by Windows and the stylus was recognised but the screen won't display anything, not even the OSD. If I unplug the cable connecting the Cintiq to the box that connects to the computer and reconnect it the screen comes on briefly but goes black after about half a second. I tried shining a light onto the screen to see if it was the backlight but there doesn't appear to be any image. I'm using a DVI-VGA cable that has worked fine in the past and have installed the latest drivers from Wacom. Any ideas or do we now have a very expensive paperweight?