I hit alt+enter to get into windowed mode. Now whenever I try to run it in full screen mode, it is just a black screen. The old mouse arrow-style cursor shows for a few seconds, so I know the screen is in the right resolution, etc. There are music and sfx when I move the mouse, so I'm sure the program's running. Also, when I alt+enter back into windowed mode, right before the window pops up, the screen flashes what is should have had on it the whole time. Is this a direct X problem? I have a HP Pavilion zd8000 with a Radeon x600 card (which I must admit has been a little buggy ever since the forced me to upgrade my drivers). Do I need to disable Dirct3D and force it to use OpenGL? When I played portal I had to force it to use a lower version of some thingamagiggy, so maybe this is a similar problem.

Same thing happened to me. I was one ball away from OCD and I pulled down the wrong one, and I couldn't hit "escape" to retry and in a moment of intense frustration while waiting through the level completion paperwork (without any ability to interrupt or retry) I facerolled my keyboard and went into windowed mode. After I alt-entered to restore, it just gave me a black screen with my goo cursor present.

hmmm... no goo ball cursor for me, so probably not the same problem. I'm pretty sure it's an ATI problem, but I don't know how to fix it. I found the config file and made it fill nearly my whole screen, so close enough.