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When I try that tool it completely malfunctions for me....doesn't do anything. I think it's a moot point though. If you previously had pagerank and now you've gone down to either 0 or N/A then there's a good chance you've got some kind of penalty. Do you have any indication of whether traffic has dropped?  If you don't have analytics you can possibly get information from your hosting company and server logs.  Pagerank (PR) really doesn't mean much...but a loss of Pagerank plus a loss of traffic makes some type of penalty a big possibility. The question is whether it is a manual penalty or an algorithmic one like Penguin or Panda. I really would advise setting up webmaster tools today.  You can either wait and see if a warning pops up or if you feel that traffic has dropped you could actually file a reconsideration request.  Google will respond back within 3-14 days and let you know whether you actually do have a penalty.  If so, then the nature of the message should help us know what the problem is.  If not, then we go looking at traffic data to determine whether this is Penguin or Panda. OR..............it's possible there is something else such as a robots.txt problem or something else going on.  But really, without some type of traffic information and without knowing if there is a warning in webmaster tools it's going to be hard to diagnose the problem.