Waterdamage, cleaned the board not switching on

Cleaning the board is not a 100% guaranteed way to fix water damage. Some times, under certain conditions, the water can cause shorts in the circuitry that cause components to fail. In some cases, it is simple an issue of corrosion on the bard, which can be repaired by cleaning the board, other times you will need a specialist to preform component level repairs. Did you only clean the main board. You may also need to clean some connectors and button pads on the inside of the phone. Corrosion can happen to any art of the phone that could have current running through it. I would go through and look for hard to see areas of corrosion and try to clean those off the see if that helps.