Iphone switching on and off

Hi fellow members,

I updated my iPhone 6S to latest iOS version 2 days before and yesterday the iPhone switched off as there was no battery left.

After connecting the iPhone to power, it switches on for a duration of 1-2 seconds with Apple log and turns off automatically.

This turn on and off is continuous and recursive.

I have tried to Update the software and also the Restore option but iTunes pops out message that iPhone can be restored/updates as the device not found.

Any help would be highly appreciated.