Sony Vaio Display Problem

I have a Sony Vaio VGN-FZ21Z, about 18 months old (warranty expired after 12). A few weeks ago my laptop screen went really dim, I could only see a shadow of the icons, when I start the computer up it the screen flickers and then goes dim. I connected an external monitor and continued to use it, now that has problems. The screen resolution the external computer won't change from 640x480 (when the laptop recognises it. At first I thought it was the laptop screen bulbs and I needed a new screen but now I'm concerned it's the graphics card, any ideas?