My iPhone 4s will no longer download apps?

A few weeks ago, my iPhone just stopped downloading applications. The weird thing is, in the App Store when I go to open one that I've tried to download in these past few weeks, it will say "open", like usual.

But I tap "open", and it does nothing. Also, the apps I acquired in those weeks are not on my home screen at all.

Is anyone else having this problem? Could iOS 7.1.1 be causing it?

Maybe because your iphone is full?