I usually build a Virtual Machine that consists of the following for SharePoint development:
I use host headers to allow the web applications I create on the VM to run on port 80. However, recently, the ability for me to visit a web application suddenly stopped inexplicably. What happened was that any web application seemed to prompt me for NTLM credentials three consecutive times, but then deny me each time with a blank page. SharePoint’s access denied page was not even rendered. Furthermore, any HTML files (images, txt, html) could not be served from the virtual directory of the web application. I found that I could visit http://localhost:portnumber sites, but no sites that used host headers.
It turns out that a recent security patch delivered through Windows Update caused the issue. There is a security update that causes any “excessive” traffic on the loopback adapter to be shut down. This means that unless you either turn off the loopback adapter security check, or place all DNS names you want to use for web application host headers under a specific registry key, host headers won’t work and you will be denied access. See the KB here:
And the recommended steps below: