Light Butons doesn't work.

i really don't understand how the buttons works, cause sometimes they are lightened . and sometimes don't.

this doesnt means i can't map on my ableton liveset the controller, in fact i map " play of track 1 (for example)" with a button and it works perfectly. but it doesnt light up . why is that ? 

so i tried to look out on the forum, i'm a bit confused. but i downloaded this : Alias8 DJ 2 Deck Project . to try on ableton and then magic! all the butons started to show up lightened. and then after that if i open a project on my own, it works good. but if i turn down my computer and start from scratch again, all is lost.