MacBookPRO5,4 Grey screen shutting down.

Hey All,

PC convert. I have had this Laptop for 18 months.

About 6 months ago, I tried to shut it down and a grey screen descended. It stated in about five different languages that I need to hold down the on button to reset my computer.
I hate it because you hear that hard drive tick and think............

Can anyone explain this one:

Tonight, I was running google chrome and writing on Garageband. Suddenly the screen went blank.
(Completely gutting for me as I had written a blinding tune).
When I touched the brightness increase button, the screen flickered on and off, to the point that I could save my efforts. When I took my finger off the brightness button the screen went blank again.

What is going on?

Run the Apple Hardware Test to see if it picks anything up. It does sound like a hardware problem and could be a number of things such as the display itself or the GPU.