A family of Microsoft word processing software products for creating web, email, and print documents.
In Word, language is a text attribute in much the same way as bold, italic or underline. If you select a single word in the problematic text and then go to the Language dialog box (Review tab > Language group > Language > Set Proofing Language), which options are shown in the dialog box?
You would want the proofing language of your choice to be selected in the dialog box and you would want "Do not check spelling or grammar" to be cleared. I would also recommend that you clear the "Detect language automatically option" for future benefit.
To fix the formatting, modify the Normal style so that it includes your desired flavor of English. You may also have to select all the text in the document (with Ctrl+A) and then (re-)apply the correct language via the Language dialog box.
See more in Suzanne S. Barnhill's article at http://wordfaqs.ssbarnhill.com/MasterSpellCheck.htm.