I've noticed that Word sometimes mysteriously turns off the spell check for certain passages of my documents (can't figure out the rhyme or reason). When I suspect this has happened, I

• press CTRL + A to select all text,
• Go to Review
• Set Language
• Make sure the "do not check spelling box is clear

In your case, you may want to deselect "check language automatically." Maybe your typing is so bad Word thinks it's Portuguese. Just kidding.