First, find out if turning the knobs has any effect at all. Put the rifle in a rigid cradle and clamp it down with the scope focused on a target. Then making sure the rifle does not move, adjust the scope knobs, trying both directions (left-right, up-down). You should be able to tell if the crosshair moves. If it doesn't, the scope is broken.
If it does, then check to see if you may have run out of room one direction or another. If so, the scope, mounts or rifle may be at fault.
Jim