Category in Dropdown list

Hi.
Could you please share a link to your site?

Yes, what is your site link? Did you use plugin for this dropdown list or the template has dropdown list feature? What is the template you are using?

i am just tried on local server there is no web link

Did you use plugin for this dropdown list or the template has dropdown list feature? What is the template you are using?

I am using twenty eleven template .i am using this code<?php wp_dropdown_categories ();?>

In that case, your dropdown box should be clickable. Make sure you are not hiding the scroll-down with a fixed height on your widgets, sections or posts.