Hope there is someone who can help me with what seems to be a below basic one, but i need help

I have a new Cateye Quick and can't turn on the computer.
So my question: to turn the dial on do i need to mount both the computer and the sensor on a bike?
I didn't think so, i was under impression that i should be able to turn on the computer just by pressing the main top (mode) button o na computer, but i am unable to do that.
I tried AC reset on the botton as well but nothing happens.
Please let me know wat i may be missing.
Thanks!