The line should be horizontal. If it's not, don't turn the thing from the moving end! Reach all the way back and turn it where it screws into the wall fitting. It is not supposed to be OMG tight, just barely snug. Also, be sure you have the controls all set properly: the thing only moves by water pressure coming out of it, so a clean filter and open air controls are a must.
Also, if the Moto runs with the faceplate off but stops once you put the faceplact back on, it may have stretched and started to rub on the back of the faceplate. If that is the case, replace the unit, and try to find out what caused the problem.
Most common cause of Premature Moto Stretch, or PMS as I like to call it, is using trichlor tablets or bromine tablets in a floating feeder. Second most common reason is overdosing on chlorine.