Yeah, you're meant to press all 4 together.
The machine won't turn on. Once you've pressed the 4 keys, wait for about 10 seconds then turn it on.
It should've reset all the settings back to defaults.
Its quite funny, I've got the same problem as you, apart from the opposite, my powerbook doesn't recognize when the screen has been shut, which is a bit of a bastard because I use an external display with it.