My printer leaves a black line vertically down the center of the paper on every print

If the line is on the back of the paper then you have a dirty paper pushing roller - you will need to dismantle the printer partially for a thorough cleaning.
If the line is on the printed side and it's there only when you scan or copy a file then the scan unit sensor is faulty. The only way to fix that is to replace the sensor and that would cost more than a new printer.
If the line is on the printed side and is there whatever the source of the printed file it means that the memory buffer from the processor of the printer has a faulty cell. There is nothing that can be done to fix that - the processor, and the entire printer with it, is dead.
Sorry, time for a new one.