Black screen with cursor and no effect

Hello,
my Acer aspire Z1 is an all-in-one pc. When I switch it on, the Acer word and a tiny circle loads. then, the screen turns black with a cursor. Ihv try so many ways to make it but it seems to not working. I remember that I just simply turn it off improperly. Last time, before I shut it down it says 'update and shut down' I hit it but I switch the power off. ya, too lazy. Help needed!!