People often think of birds as ornaments that can be kept in cages to look pretty, which is very unfair to the birds. They need a lot of attention and interaction. Screaming is also a very natural behavior for birds. These sites may help:
http://www.quakerparrots.com/trainin...creaming-help/
http://www.ozquaker.net/index.php?i=22&mg=t
http://quakerparrot.org/quaker-parro...ut-of-control/