I can't open my Pages app

I have recently bought a new Macbook Pro and I'm currently running OS X Yosemite version 10.10.3. I can't seem to open up my Pages app. I have just updated my Pages app in the App Store to version 5.5.3 but when I try open the app from my applications it won't open. The applications window opens up as it wanting me to select an app but there is no Pages option available to select. Can someone please help me?