why i can't take a screen with LG nexus 5 I'm trying to take a screenshot on my Nexus 5 phone following the obvious instructions, which instruct me to press both the down button and the power button at the same time.. nothing happens.

I remember in my previous S3 phone there was some some setting that had to be turned on to enable swiping gestures to take a screenshot.. but i couldn't find anything of that sort with the nexus 5.. any ideas?
Android's hotkey to take screenshots is Vol Down and Power pressed simultaneously for about 3 seconds.

The delay is there to prevent accidental presses.

( Samsung phones hotkey is the Power and Home button )