I have an old Macbook Pro (2008) running Leopard that was having intermittent black screens during operation that wouldn’t go away (not ever after a reboot). The external DVI port would still work, and I passed the GPU tests related to the Apple Nvida GPU issues (TS2377).
My fix was to change the screen resolution via an app called cscreen. It’s hard to find the .dmg file, but not too hard. I wrote some apple script that changes the resolution and colour depth, compiled it as an application and put it in my applications directory. This way I could find it in the “dark” with spotlight by pressing command-space then typing my app name and pressing enter. Interestingly enough sometimes just pressing command-space would bring the screen back to life (but nothing else seemed to).
Glad to have a work around, but it still seems a weird issue.
The link to the article that go me on to cscreen is here.
Update: This solution didn’t last long and the laptop died – I suspect it was the known GPU issue with this model, but Apple denied it (Sydney Apple store) and can’t run the tests as the laptop is dead. Sniff.