Laptop screen looks like an old fashioned TV test card

G'day

I was working on the net on my Macbook Pro (OSX version 10.8.3) when it suddently started displaying a very fuzzy screen a bit like the old fashioned black and white TV test cards of the 1950s. All that I can discern is the Apple logo, but it's very vague.

I shut it down and left it for 10 mins and fired it up again, but no change-help...

John Mc