Maybe it’s highlighted. Check on your formatting toolbar for a text that has a colorblock through it.
The hightlighting tool is next to the text color tool on the formatting toolbar. Make sure you always have the formatting and standard toolbars up at the top of your document at all times Go to View—>Toolbars—>
Make sure the top two are checked (Standard and Formatting)
This will keep your toolbars visible for you at all times.