1 inch horizontal black lines on my nokia 6300 cellphone

Jst keep ur mbl in low temperature and only use it for call dont use it much. It will disappear soon

It sounds like a faulty screen matrix this is not repairable you must replace the screen. If its under warranty it will be covered. If not the screen replacements are only $24 Australian + postage. You need to know somone a little tech savvy to install it if your not keen yourself.
Hope this helps