Why Did my Phone turn off while I was using?

I was using my phone and suddenly it turned off . Total Black out . Charging was 80% and was not Overheating. I thought it was the screen but I've got it checked out and the Screen Panel is totally Fine . Then why did it turned off and is still not turning On ?

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Did you just happen to be using it in a particularly humid environment when you were using it

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It works when I'm connected to WiFi but it becomes an overdose and turns off. This is a challenge for me. I need a solution. I'm in Tanzania. It works when I'm connected to WiFi but it becomes an overdose and turns off. This is a challenge for me. I need a solution. I'm in Tanzania.

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