Also don't download so much all at once.
Obviously if you download 50GB, it will be difficult to seed all of that back to the community.
But what you are saying is your torrents are not seeding.
So here is what you need to do:
a. check your settings in your client, make sure your seeding settings are actually enabled, etc. Consult the FAQ for your client (i.e., UTorrent, BitTornado, etc.)
b. check to see that YOUR PORTS ARE FORWARDED http://portforward.com/
c. check to make sure that your firewall is allowing seeding http://btfaq.com/serve/cache/25.html
d. check to see if your Internet Service Provider / internet source isn't blocking you. This is especially possible in the military or in many universities, that interfere with bit torrent data.
