Cannot install apk files

[GerGa]

I have an s4 stock att version and trying to install apk apps. I open the file, it asks if I want to install with all the permissions. When I click install in bottom right corner, the button does not press. I can however hit the cancel button.
Am I missing something?

Thanks

 

[N4Newbie]

Not entirely certain about Samsung's android skin, but check Settings -> Security -> Unknown Sources.

But, I hope you know exactly where that apk came from and are certain that it is not carrying malware...