I had (and still have) this annoying problem, {Win 7-64 bit} but by going over a number of remedies from several sites, I found a simple fix that works for at least your current session.
Fire up Task Manager and close the 'Process' called "explorer.exe", which shuts down all programs and window features except the Task Manager you are still in, so VERY IMPORTANT - Do nothing else but go to 'File' and select 'New task' and type in "Explorer.exe." and everything re-appears, but task bar stays hidden until needed as it's supposed to do.
Most times it stays that way for next session, but if not just do it again; at least that works and it's not too hard to do once you get used to it.
~ Dave \W/