Laptop is on, but screen is black.

I don't have the 8600 though, mine is newer and has the 9400m / 9600m graphics cards. 1850 numbers aren't free here, I'll have to give them a call though. It just keeps coming on and off. I shut it down the other day and it wouldn't come on for another full day. It just kept showing the white sleep light at the front. It's as though I shut it down, and when I turn on it enters sleep mode rather than booting.

Interesting...
I came here to post the problem I was having only to come across this thread that outlines my problem 100%.

My computer was on just fine, closed the lid to get ready for bed, remembered I had to check something else on the computer, and boom, screen was black but it still seemed to be on. The computer no longer goes to sleep when the lid is closed, and I've tried restarting, keeping it off for a while and even plugging in an external display but nothing works.

Only difference here is that I have had my logic board replaced once for an unrelated issue about a year ago, and now this is happening. I know there's an extension to the warranty based on this issue, but I'm worried that since I've already had my logic board replaced that they won't do it again for free...

Any thoughts?

I just got back my MBP from Apple. Thankfully it was a quick turn around. What will make it quicker if you already have your own backup so they can send it out right way. Otherwise they will perform a backup before sending it out. Anyways, Texas tested and replaced my Logic Board. Been running for 8 hours now and my MBP has gone to sleep and rebooted without any issues. Knock on wood. The one thing that I do notice is, the sleep light had stopped pulsing and stayed bright white even when it had gone to sleep. I also saw the Sleep light stay Bright white when I booted and that is how I also knew I was going to get just the black screen. So aside from the Graphic card issue it seems there is a logic board issue perhaps as well.

So if you do come across this thread because you are having this issue I would print a copy to bring to the Apple Store and tell them to not waste your time having it tested there but insist that they send it off for repair and believe it is the logic board. If your symptoms seem the same as all these post, You wont find a solution I believe to fix the problem yourself, don't waste anymore time and go send it back for repair.

This is a common problem with the macbook pros, caused by the faulty NVDIA card, causing the logic card to fail. Find an authorized apple repair shop that knows what's up, not the apple store (their "geniuses" run a test that only checks the video card, which might appear ok, but does not reveal what it has done to your logic board), and they will fix it for free. see this link for more info:

http://www.pjentrepreneur.com/2009/01/21/update-mac-book-pro-blank-screen-proble m/