My 2012 Ford fiesta se can't go reverse

I drive a 2012 Ford fiesta se and it can't go into reverse and
the engine light is on. It can start, which is now starting not
to do, And it can drive. We disconnected and reconnected
the positive and negative battery cables. The problem and
the light was gone. Until the next day they  both came back.
We thought it was the transmission fluid and the negative
cable. We had to get them both replaced And reconnect the
battery cable And The problem where it can't reverse and
the engine light was gone and the car was working again
until the next day they came back. While it was doing this
the car was having a hard time starting but it does turn over
like sometimes. We thought it was the starter or the ground
cable but do you guys think?