It have to has its coordinates changed to some out of screen values. If that is the case, then one of the solutions would be to changed them directly in database. But other good solution that could also protect against it in the the future is to use 'Start position' plugin. From tray you have access to main menu so you can download it using PluginUpdater downloader (Main menu -> available component list). After that you could be able to set position of your clist in options under 'Contact list' tree. Just set like 0 pixels from top and 0 from left (or whatever best fit you) and should work. Probably restart of Miranda would be needed.
