Don't ever put battery before cleaning the board. First disassemble all parts. Take pcb ie board apart and you can clean it with thinner or white petrol. Take a tooth brush and dip it in thinner and clean the board gently. Try to clean the display touch and other connectors with care. Now take an hair dryer and set it with heat set. Now slightly heat up the board . Then assemble the parts and switch on the phone 75 percent it will switch on..