Oculus Rift doesn't work for demo application

Question

I'm trying to develop a game in Unity with Oculus Rift. I have DK1 as my environment. I have a game called RiftCoaster as demo and it works fine but the default demo in Oculus rift doesn't work. The demo unity projects I download from Oculus doesn't work as well. What might be there problem? Although it works with some samples I couldn't make it work for Unity projects of default demos.