A bit of googling suggests this is a known issue and especially common if you're trying to play this game on a computer with a low-powered graphics card. Do you know what sort of graphics card your PC has? There is a workaround for the issue on the developer's website here; have a go at that (or come back if it doesn't make sense and I'll try to explain!) but the ultimate problem may be the graphics card.
Thank you for your reply. I'm sorry I did not return to the thread . I did try the workaround. I then emailed Steam but heard nothing after an automated message. Will try again but don't hold out much hope.