Unable to get anything except 403 from a .Net 4.5 website

I had a similar problem. This thread https://stackoverflow.com/questions/2374957/asp-net-mvc-on-iis-7-5 solved it for me. Basically try adding this to your web.config:

<system.webServer>
    <modules runAllManagedModulesForAllRequests="true"/> 
</system.webServer>

If that work you can try removing it and install this hotfix instead: http://www.microsoft.com/en-us/download/details.aspx?displaylang=en&id=5272