A family of Microsoft word processing software products for creating web, email, and print documents.
You've merely toggled off the display of what Microsoft refers to as White Space, i.e., the top & bottom where Headers & Footers normally display.
Position the pointer on the top or bottom edge of the page. When it takes on this appearance double-click to toggle display of White Space on again. This also can be controlled in Word> Preferences - View.
BTW: For future reference please don't jump the gun by reinstalling the software. That's a hack that works on Windows PCs but isn't the same on a Mac. It's a last resort & requires full removal first i order to have any hope of succeeding. If not done properly it can cause more harm than good.