Why Samsung GT-S5570 Mini not turning on after pressing the ON switch?

I have a Samsung GT-S5570 Mini which was bought in 2014. I was able to use it until February 2018 when it no longer turns on due to problems with its ON switch. Sometimes the ON switch works but most of the time the ON switch won't work.

Now come February 2023. I turned on the Samsung Galaxy GT-S5570 Mini and alas! It turned on! It seemed not to have problems for few days but it seems the problem with its ON switch starts to creep up. I even need to strongly press the ON switch to turn on the phone.

Few weeks ago, my Samsung GT-S5570 Mini phone wouldn't even turn on even if I recharged her batteries.

I bought the Samsung GT-S5570 Mini to the repair shops and they all said that there is a problem with its board, but they couldn't pinpoint where is the problem in the board.

Why is Samsung GT-S5570 Mini not turning on after pressing the ON switch?

Thank you for your help!