Iphone 4 won't turn on

Hi

I hav an iPhone 4 that won't turn on and also gets hot when charging

I've tried the reset and nothing !

I've tried to put in dfu mode and nothing it fails.

I've tried a new screen , still nothing

I've tried new battery and also tried a new proximity sensor

With no luck !!

I've tried stoppin and starting the apple services in control panel and also reinstalling the drivers, still nothing

Tried a new charging port and nothing works !!

The mother board just above the charge port connected gets really hot when charging so I'm beginning to think this is where the problem lies

Any advice will be appreciated

The only warning I get is when plugged into the comp it comes up with a warning that the USB device has malfunctioned please try unplugging and pluggin it in again

Help please !!! :-(

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