galaxy A8 rebooted itself automatically and keep on downloading even i am not able to switch it off

[AC Question]

screen shows only downloading some more details are showing on the top left side and not performing any other operation

 

[B. Diddy]

Welcome to Android Central! It sounds like you're in Download Mode, aka Odin Mode. Force a shutdown by pressing and holding Power and Vol Down for 10-15 seconds, then power on again normally. Do you keep arriving at that screen?