Follow the instructions on screen. Some people might say it's entirely based on the last question, or that it's pointless; it's not. Harry Potter was asked this and placed in one of his choice but Neville was too and was not placed in what he chose.
DON'T PRESS SPACE!!!! OKAY NOW I GUESS YOU'RE GONNA PRESS IT. OH WELL. It's slightly glitch and it may not tell you your house. If that happens, take the test again and vary your answers.