There is a big black verticle line on the screen

Vertical lines in general are caused by the data boards (buttom of screen) theres a left one and right one these boards are atached by ribbon cables going to the logic board .first all ribbon cables must be checked and reconnected to make sure there well seated ,also pass compressed air ( can ) , if this dose not solve problem try slightlypressing on the connecters replace defective board , on many lg tvs the connecter on the logic board is defective slightly pressing solves problem ,if this does not work you have two choices the data board thats on the same side of the line is defective you may try to clean the brown flex connecters that plug to the data board these connecters are not easy to reconnect be delicat and patient !!!if data board does not solve replace logic board !