starting the Samsung A8 and half a line at the top will not turn on fu

When I power on the Samsung A8 the startup screen with Samsung A8 comes on for a sec then a thin coloured line at the top appears and it shuts off again. Can you help? I have tried holding down the vol down with power, vol up with power and vol up and down together with the power button..then it brings me to OS download page..but won’t do anything.