Screen Display On and Off

Hello,

I'm using a Macbook Pro which was purchased in 2008.

A few weeks ago, my laptop screen blacked out while I was using the Internet. I knew that my laptop was running because the audio was playing but the screen basically blacked out. Apple ran a test and said it's a logic board failure and the graphic card is still working fine. I've been using my laptop via an external monitor but my laptop screen started working all of a sudden just a few minutes ago. ... But it blacked out for a minute or two and started working again. Maybe it's only a matter of time before it blacks out but why is this happening? Any ideas? Apple said that the faulty component by NVIDIA is not the cause of my screen display problem, so a repair cannot be done for free as stated in this article: http://support.apple.com/kb/TS2377

So any ideas why my laptop screen is working all of a sudden after blacking out for a few weeks?

Thank you.