If your files have extensions that read .001, .002, .003, etc. then it has been split into pieces and you need to rejoin them to watch it. Personally, I use a little freeware program called HJ-Split to rejoin split files of that type.
you need to give more information for us to help you. what is file extension of the file you're having trouble opening?
or provide us the link at akiba-online where you downloaded the torrent