We have an unusual problem with one of our websites, Google has dropped the index page from the results. Internal pages are ok and have good PR. The index page has the "grey bar" and no longer ranks for any major terms, over the last couple of months the index page has been in and out of the results Yo Yo style.. We can't see any evidence of hacking or server issues. The site is a static site on the front end with information blogs on a few subdomains, they continue to perform well and rank well. Looking at the index page it looks perfect, I can't see any logical reason for this.