LED do not light up

[grandgooroo]

hello !
I received the Raspeberry Pi Zero but LEDs do not light up. They lit up steadily and only a few of them, and now they don't light up at all.
The cable connectivity is good (tested with a multimeter) but I may have made an inversion somewhere !?
On the LED strip, Red = 5v, Green IDI.
http://onirike.free.fr/tmp/P1020173.jpg
http://onirike.free.fr/tmp/P1020172.jpg
http://onirike.free.fr/tmp/Piano%20LED%20Visualizer.jpg

[grandgooroo]

I entered the wrong direction for the LED strip, to be tested.
[Edit]
That was it. However, when I press the midi keyboard, one out of two LEDs which lights up. How can I configure this? Currently it's a 50cm strip of 72LEDs. Ok I check if "density" solve my problem.