Why does my engine not turn over?

It wasn't going into gear. You push in shifter button and nothing. So we pulled the shifter casing and saw that an pin wasn't engaging and wouldn't let it go into gear. So we manipulated it by pushing the little pin in to unlock shifter and be able to out in gear. The little motor or solenoid  is 400.00. So they went to pull n pay and took whole thing. Shifter casing solenoid.  Installed it. Drove it. It ran cherry. Went home turned it off and it wouldn't start again.