no signal on headphones on hercules dj control instinct

hi, i just got started with my new hercules dj control instinct controller, but the pre-listening function doesnt work. whenever i push the headphones button on any of the 2 decks (and they are lighting then) ,i hear no signal on the headphones.

i use a normal 3.5 mm connection cable which i put in front panel. the headphones are wireless ones, might it be connected to that? have no idea of what to do anymore, pls help me to get on peeps:/

thx

nik