The LG G4 was released in the US in early June 2015, as always focusing on high-end specifications and a refined fashion sense that makes it stand out in the premium smartphone market. Each version of the phone will have a different model number based on if it is sold by a carrier or sold by LG as a US Unlocked or International model.
Use this guide, clean the logic board with 90% isopropyl alcohol. Don't use anything less. Then try turning your phone on. It's likely something will be damaged. Probably the battery, or charging dock, or display