You have to restart the explorer.exe by hitting CRTL+ALT+DEL and click Task Manager or Windows Key + R and enter taskmgr and OK. Then under Processes find explorer.exe and End Process. Then click File, New Task (Run) and type explorer.exe, OK and the Taskbar will be restored. This is behavior from 3rd Party Screensavers that Windows does not like. So customizing screensaver with Irfanview to run Slideshow Play Mode in Play in Window works for us.