Please go to one of the words that you know is misspelled.
Click in it.
Then press Shift+F1.
A pane about Reveal formatting should pop up.
In that pane, does it say "Do not check spelling or grammar" under Language?
If so,
Press Ctrl+A
Under the Review Tab
Language
Proofing Language
Uncheck the box for "Do not check"
That box must be clear.
Then press OK.
In the meantime, here are some resources.