i cant mine

when i go into minecraft and create a world i can put down blocks but i cant mine them.  i tried this in all the game modes, survival, creative, and adventure and its the same problem in all of them.  I can put down blocks but i cant mine any blocks, i cant get rid of them.  i made a couple worlds, and the problem happened, so i deleted them, and i made new worlds, but the same problem occured, i cant mine!  i dont know what to do now, so i am just kind of giving up.  As you can see in the video I can place blocks. But I cannot destroy them. I was trying and trying but nothing is working