If you've just installed PHPList, but when clicking compose message, no textbox appears, you'll need to apply the fix listed on this page
http://forums.phplist.com/viewtopic.php?f=24&t=24497&p=61972#p61968
If you are running a version beyond 2.10.10 please try this fix
http://forums.phplist.com/viewtopic.php?f=24&t=31546&p=75287#p75287
