Why does my tablet notreact when I touch the screen or home key.

I am touching the screen it does not do anything. But when I press the double square key to the left of the home tab it brings up all open windows. I can also press the power key and it gives me options to restart or turn off and I can use the volume up and down keys on the side. But can't do anything with touching the screen. It is stuck on some blue diamond image with gold and silver dollar signs all over the front cover now after I plugged it in the computer. screen has no scratches dents system always stays in case. Cant do anything including stopping the alarm from going off that I set last night.