Ah, welcome to “Tiny Footprint Mode“.
This mode exists for geeks who want to put a little CPU meter in the corner of the screen. To go back to normal mode, just double-click any empty space in the border.
This is one of those geek features that has created more problems than it solved. Sure, the geeks get their own little CPU meter in the corner, but for every geek who does this, there are thousands of normal users who get into Tiny Footprint Mode and can’t figure out how to get back.
Exercise: “I can’t close my apps using Task manager. What do I do?”