Did you turn the glasses on? The 3D Vision 2 glasses have a button on the left side, at the back side of that silver plate. Make sure that is pressed.
I've read some funny behavior on the ASUS 3D Vision 2 monitor, which cause it not to enter 3D Vision mode, but trying again usually fixes it.
I'm pretty sure they're turned on. I press the button on the left side and a green light turns on for about 30 seconds.
Then after a few minutes, one of the lenses flash a five times (I guess they're turning off).