datepicker

hi,
i am using jquery ui to get date picker.
below is my code
$("#maday").datepicker(
{
showOn: "button",
buttonImage: "images/icons/calendar.png",
buttonImageOnly: true,
dateFormat:"yy-mm-dd",
changeMonth: true,
changeYear: true,
}
);
i can see datepicker with #maday byt when i click on year or month,
the dropdown dosent open
please let me know what is wrong.
regards,
saurabh