Unhealthy Green Apple

This is just about all I can get out of my Macbook Pro now - as soon as the first stage of booting completes all I get is a grey screen. It is extraordinarily difficult to make a booking at the Apple Store, and it only offered me ONE possible date to visit, Friday next week, which is impossible for me due to a medical appointment. This is an early 2011 MBP, so it's a common problem, but heaven knows if I shall ever manage to get it fixed.