Macbook Screen Brightness Drops Randomly

Hi, I have following problem:
my Macbook's (purchased about 2 years ago, no problem so far) screen started to turn black. It is the back light for you can still see what's on the screen.

It turned out that screen brightness drops to zero. It can be temporarily fixed by pressing F1, going with brigtness all the way down, and than F2 up again, when it starts to gain brighness again as it should.

It occures randomly, can not really be reproduced. I have tried creating a new color profile, did not fix, tried unpluging, removing the battery and holding the turn-on button - no improvement either. Tried to change the screen sleep setting - nothing.

Any help, at least leading towards figureing out if it is hard/software problem, would be greatly appreciated.

Thanks a lot.
M. Rejsek

First thing that comes to mind is whether you've installed all the latest software updates on your Mac. Have you?

Yes, it could be a hardware problem. Before you settle with that, run some regular Mac maintenance. Pop in the DVD that came with your Mac and start from it. Once it starts, run Disk Utility from the disk and repair permissions as well as Verify Disk. Then re-boot your Mac and see if that solves the problem.

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I did not try the intall DVD, but I ran the dik utility and also applejack. No problems with the disk found. Software update also claims that my macbook is up to date.