That normally means that the battery is totally dead and needs charging before the iPhone can turn on. Try charging it for several hours to see if that makes a difference.
Turn the phone off and place it in a bowl of rice for a few days. It may or may not come back to life. Most of the time they will, but there’s always the chance it won’t.
from what ive seen its the mineral deposits that are left on the board after the moisture has evaporated thats the biggest problem, ultra sonic cleaning then industrial alcohol needed maybe chap