i think its because you left out the expire time. make it something like this:
setcookie("sessName", $row_rsLogin['username'], time() + 3600);
but if you want the cookie to last longer change the time and if you want it to expire when the browser closes, just leave time() with no number after.
edit nevermind, that is permissable to leave it out. have you checked in your cookie folder to see if it is actually there and php just cant get it back? last night i spent over an hour messing with cookies because i was setting one with a dot in the name and mozilla showed the cookie existed with all the right information but php couldnt get it back because of the . in it.