The menu and management tools are missing. I can’t change the window size. OS-Windows 10.
I can think of two things:
You’re using Full Screen mode. It can be turned on or off using F11. I don’t believe this is the cause, but it’s worth trying.
You’ve opened Word or other Office program, then this black ribbon appeared on top. I believe this is the cause.
To check and fix it for the moment (until you open another Office program), right click on a clean area of Desktop and click on “Settings” (Exibition settings). Then change scale and layout to 125% and change it back again to 100%. (You can also change screen resolution anc choose “Revert back” on popup window).
(As I’ve freely translated from my Brazilian Portuguese Windows, menu and options can be different).
To correct, apply the following resolution:
a) Open any Microsoft Office program.
b) Click on the File tab in the upper left.
c) Select Options from the left navigation menu.
d) In the popup window, select Advanced from the left navigation menu.
e) Scroll down to the Display section and check the box to Disable hardware graphics acceleration.
f) Click OK.
g) Close all Office applications.
h) Restart your computer.
“Source 2” bellow has a second way to correct, using Regedit. There’s some issues about changing Windows Registry and you can broke some things in Windows, so I prefer not to use it unless there isn’t other way.