CD key generator was included in the torrent download. Look in the download directory. If it doesnt play, then the DVD may have become faulty or encoded incorrectly.
If you really want to watch the movie HOW HIGH:
I assume that this is the movie:
http://www.imdb.com/title/tt0278488/
I have a download link:
http://isohunt.com/download/10588665/How+High