Can't arrange icons by "last modified"

Hey everyone, i am having some problems with arranging my files by last modified. At the moment they are in tiles format and then when i try to arrange them by last modified....that option is not available. It use to be because thats what i have always arrange my files as. I have tried switching to different formats such as thumbails and icons but the open to rearrange by last modified still isn't available.
Here is a screenshot. Hope someone can help me. Thanks in advanced.

 

open up windows explorer choose view then choose "choose details" then make sure "date modified" is checked off