Network: The sign up page is not display normally

Assistance pls, from the sign up page theres is two field for site domain that lay beside one another, one is where user can enter her username to be use as subdomain to create site and the other one is a field that display the site domain either as text or drop down (in case for multi-domains) field but in my own case it only display one text field for user to enter here username or subdomain to use to create site the second appear at the bottom just below create site button. the screenshot is attached here below for more explanation: the frommysite.png is the screenshot from my site and normal-setting.png is a screenshot of how i think it suppose to be….thanks in advance