I think it is the mother board issue
My redmi 2 could not connect to the camera after I spot that I shake the phone when I switched on the camera app, the screen flash blue in less than 1 second.
I took it to Offical Xiaomi HK to fix it .
They just said that the motherboard was not functioning correctly.
They just replaced one for me.
But I think I will face the problem again…
(Sorry for my bad English…)