Got F1 visa in 2008 but did not go to US now apply for same in July 2015.

I have been issues F1 Visa in 2008 but I did not go to US. Now I am applying for F1 visa again in July 2015 in case if the VO asks why I did not go to US in 2008 what would be the best answer please suggest very urgent

Well, you should tell the fact of why you did not go to US. There is nothing to panic, you can always tell about your work or family situation on why you could not go…It should not really impact your current visa stamping chances.