Screen turns off at lid opening When I close the lid, the computer behaves correctly:


Screen turns off  
Does not go to sleep (front light stays on and does not flash)  
Still can hear fans


It behaves this way because I share my wired network connexion via Wifi (System Preferences > Sharing > Internet Sharing).
When Internet Sharing is disabled, the computer goes to sleep and at lid opening, I don't have the problem described below.

When I open the lid:  


The screen turns on...  
...and turns off about 2 seconds later


I can see my desktop background and the login screen for 2s, and after that the screen becomes black (actually it really turns off, that's not backlighted black).

The little trick I found is to reduce the luminosity thanks to the F1 key, and then increase it again to come back to maximum luminosity thanks to the F2 key.
It's not really handicapping since I found this little trick, but it's a little bit annoying to have to do that every time I open my Macbook :(


  Computer specs :
  - Macbook Pro 15" bought 2 months ago
  - It came with OS X Lion already installed
  - I choose the screen resolution option (don't know if it matters)



UPDATE : Doesn't seem to be a problem any more in Mountain Lion.
There is a similar discussion on discussions.apple.com from which I picked the hint to run

pmset -g assertions


to list a summary of power assertions. Assertions may prevent system sleep or display sleep.

In my case I had a print job in queue that was preventing sleep.