hx711 and half bridge load cell

hey there i have some trouble with my hx711 and the half bridge load cell . i have a load combinator , a hx711 and 4 half bridge load cell and i have connected them all and use the SparkFun_HX711_Example by sarahalmutlaq code and i don't get a correct weight from it , it goes up and down with out putting anything on it . has anyone a idea why ???