fadeIn() not working

fadeIn() not working

I don't get it. This code works:

fancyLogin.dimScreen = function()
{
   $("body").append("<div id=\"fancy_login_login_box\"></div>");
   $("#fancy_login_login_box").css({"position" : "absolute", "height" : "50%", "width" : "50%", "top" : "50%", "left" : "50%", "background-color" : "green   ", "z-index" : "3", "opacity" : "0"});
   $("#fancy_login_login_box").fadeto(2000, 0.5);
}


But this doesn't:

fancyLogin.dimScreen = function()
{
   $("body").append("<div id=\"fancy_login_login_box\"></div>");
   $("#fancy_login_login_box").css({"position" : "absolute", "height" : "50%", "width" : "50%", "top" : "50%", "left" : "50%", "background-color" : "green   ", "z-index" : "3", "opacity" : "0"});
   $("#fancy_login_login_box").fadeIn("slow");
}


Why would fadeTo() work, and fadeIn() not work? Can anyone give me a hand?