mikey, the very first thing I suggest is that you do not turn your iPhone on. If you truly used salt to dry it out, I would disassemble it PDQ (pretty darn quick) since water and salt will corroded your logic board and components really quick. Once it is disassembled ( use this guide) clean it extremely well in 90%+ isopropyl alcohol. Do not forget to clean all the connectors and cables as well. Clean it multiple times, use this guide to clean it. It was written for a 3G but still applies to your phone as well. Once it is cleaned, replace the battery and reassemble. Check for any further damage. The backlight is contained in the LCD, so it is possible that replacing the LCD will resolve that, but it is also possible that it is your backlight coil or your backlight IC, So start by cleaning it, after that by replacing the LCD. Of course make sure that you check your board for any burned , corroded or missing component.