Help needed, Macbook Pro dodgy LCD wires?

My 15" non-unibody Macbook Pro was acting up for a little while. Flickering screen, then after a day it went black altogether.

However when i change the brightness the screen gets dimmer/brighter but just no image. I connected it to an external screen, no problems, all working there. Took it to the Apple store and when they turned it on it worked flawless for a couple of minutes but then died again. And they seemed to think that the LCD could be bad but I was out of warranty. So i decided to take it upon myself. Bought an LCD from a legitimate online retailer, fitted it this afternoon and still no joy. Can anybody shed any light on this? Could it be one of the wires to the screen or something more serious?

Thanks

Wires or video board are the most likely components... One is kinda easy to fix if you don't mind disassembling. The other? Well... can't be fixed.

I've already got the machine in bits so don't mind getting involved but don't want to waste a load of money if it turns out to be something unrepairable. Is there any way to test the video board? Like I said it works on an external monitor, it has been into Apple and they seemed to think it was a panel issue. I've bought and tested a new panel but nothing so I guess that cancels that out?

The Apple report said -

"Issue:Boot machine, video signal is black, External monitor shows correct signal, can see desktop and meny bar and all data is loading fine. Appears issue is with panel. Reset SMC and PRAM with no change.

Ran GFX tester and once rebooted ran it again, during second run through display came back on. CMR reports originally display went off, and did come back on again, but only for about 10 minutes before reverting to video black"

Thanks