This morning I installed 10.5.8 on my Santa Rosa MBP (2.4 Ghz) after having made sure there were no weird issues with it (by reading this thread). However, after reboot the screen stays black. Not only the backlight is off, but also there is nothing on the screen (checked the screen in full sunlight).
I turned it off, took the battery out and unplugged the cord an turned it on to make sure it was really off, but that didn't help. Resetting PVRAM didn't help either.
I tried to boot the Leopard DVD (c key pressed) and it looks and sounds like the DVD boots properly, though still nothing on the screen.
Last week I installed rEFIt in order to boot Linux from an USB stick, not sure if that has something to do with the issue. One would still expect the screen to light up and the apple logo to show...
If the issue is related to rEFIt it might be that the Mac does not boot from HD, however you would expect it to be able to boot from DVD and that it would show the Boot screen (Grey screen with mac logo) properly. I do hear the bootup sound though...
So, now I am at the Apple store where they had a quick look and hooked my MBP up to an external monitor, no luck either. They only tried to boot it from harddisk, so I am going to find a friend with an external monitor to try to boot from DVD and see if that will show on the external monitor.
Anybody experiencing similar issues?
I have the same model as you and yes, known issue with these. Your graphics chip crapped the bed.. You need to have apple warranty it for you. They'll replace the logic board..
http://support.apple.com/kb/TS2377
Good luck