HELP PLEASE! Macbook Pro will start up but with no video.

Does the icon show on the screen when you're changing the brightness? Try booting in to safe mode and see if it will display anything. If all else fails, contact Apple or make an appointment to see a Genius at your local Apple Store.

With my amazing experience with my "old" MBP, that I just got rid off, here's my 2 cents:

I had two issues concerning not being able to see the screen.

1. You cannot see the screen at all, not even by squinting or shining a flashlight. If you connect the MBP to an external screen it still won't display anything.

If this is the case you're GPU card has failed. You will need a logic board replacement.

2. You cannot change the brightness of the screen and it seems stuck on the lowest setting. You can kind of make out that desktop and can see it better if you shine a flashlight. If you connect the MBP to an external screen it will behave normally.

If this is the case here are some of the possibilities:

A) The screen backlight has died (will need to replace the screen)
B) A cable has come loose (Depending on the reason why it came lose it can vary from simply reconnecting it better or replacing the logic board/cable).


Cheers.

Most likely, the GPU failed. The old 8600M GT cards from nVidia were defects so Apple should replace it for free.