today I attached Reprapdiscount Smart Controller to arduino mega and did first moves with Z axis. What is strange that if I move for example possitive 10mm Z axis move normally, but
after setting to 0mm it does not want to go back. What do I wrong ?
Nothing. That's what especially the Z axis isn't allowed to do: Moving in negative direction below Zero.
You can define a manual overrride to allow that, but in general it is best to leave it like it is.