When I try to install the game on my system the install button on screen is not clickable? No mater what I try to do. Do I need Crysis itself installed in order to install Warhead? It's the only thing I can see that could be wrong as I don't currently have Crysis installed right now.
It is supposed to be stand-alone (I had the original installed). If you have Daemon Tools running, disable it. EA's Securom DRM is notorious for not allowing you to run/install with .iso programs running.