my samsung galaxy note 10.1 is frozen on the Samsung galaxy logo

My tablet is frozen on the Samsung galaxy logo. I tried holding down the power button but it just goes blank and goes back to the logo. I tried holding the power button and the volume up button and it still does the same thing, then I tried holding the power button and volume down button and it took me to this screen about downloading a custom os. It told me to press volume up to continue and volume down to cancel so I pressed cancel because I don't know anything about downloading a custom os.