blackburn atom SL 3.0 bike comp

[roadmaster]

Hi guys I'm a newbie to the cycling, I have a road bike with the above comp the problem is I can't seem to sync the comp with the sensor also it does not want to pick up the id no of the sensor. Have changed batteries on the sensor still no change went as far as testing it on a another unit exactly the same as mine but nothing. Pls advise.have the unit just over a year.