It fell in water. It may turn on for a while and then die.
Corrosion on the board. The damage keeps spreading as long as moisture stays inside.
Don't turn it on, don't charge it. We disassemble, pull the battery, ultrasonic-clean the board in 99% alcohol, dry it, and only then test.
It depends on the model and on what we find inside, so we quote each repair individually. The diagnosis fee depends on the device, and you approve the exact repair price before any repair starts. If it can't be fixed, you only pay the diagnosis.