Help browser not showing

My help browser doesn't appear any more, either from the menu help/igor help browser, or the keyboard shortcut cmd+/. I think this has been the case for a few days now.

The context menu help all looks to be there if I right click on a key word, but I can't browse e.g. command help. If I scatter the open windows using a hot corner, then a window label for the help shows up as open, but there is no window associated with it.

Any ideas why this might be the case? I've restarted Igor, and the computer.
Try selecting the Windows->Control->Retrieve All Windows menu item. If that doesn't work, try the latest nightly build (http://www.wavemetrics.net/Downloads/latest/). There was a problem that we fixed not too long ago in which the help browser windows somehow got to be very small, like 1 by 1 pixel. I don't remember if the fix was before the last official release, so that's why I recommend the nightly build.