I've now had chance to try installing the official Nvidia graphics drivers as well as the various graphics and chipset drivers provided by Dell and Intel, and the problem remains.
What I don't understand is why when you delete the driver for the HD4000 graphics built into the Ivybridge processor, Windows doesn't fall back on the Geforce 620 1GB card that supposedly came with the computer. Windows identifies that it exists under device manager, but instead defaults to its standard VGA driver when not using the HD4000. It shouldn't matter that there's an issue with the HD4000 if there's a better card already installed I can switch to. What's even stranger is that the technician told my mum she doesn't have a graphics card.
