My Process Explorer view got messed up a while ago. The process tree view wouldn’t display any more no matter what I did in the View menu. At the time I searched for solutions on Google, but found nothing.

Today I repeated my search – and Google found a site that mentioned the same problem: http://west-wind.com/WebLog/posts/9849.aspx

The solution was given by Matthijs van der Vleuten in the comments of that post: Remove the ProcessExplorer registry tree. You’ll have to reconfigure everything in ProcessExplorer afterwards, but that’s a small price to pay for getting the tree view back.