Problem
While working on a project, I had left my computer on to go grab some dinner and when I came back, I attempted to use the Rectangular Marquee Tool, but all I could see was a hand. I tried switching tools, for some reason I was still able to lay down guides, but I couldn’t move them, closing/re-opening the file, restarting the application, and then I finally searched online and found the solution.

Solution
Try changing the workspace from the Window menu. I changed it to “Essential” and that brought back all my functionality