A family of Microsoft word processing software products for creating web, email, and print documents.
I see that there are two entries for "English (United States)" in your Language dialog box. The first entry has no check mark next to it, which suggests that proofing tools are not installed.
The second entry does have a check mark. I have to admit that I haven't seen that before and I'm wondering what could be the underlying cause.
Above the horizontal line in the list of languages is the recently used languages. If you scroll down to "English (United States)," do you see two entries there as well?
One more thing: Note that every time you select a sufficiently large range of text, the "Don't check spelling or grammar" will be a filled box. In Word, this is normal for large selections. You'll see something similar for the "Font" setting if you select several pages of text in a document; even if the whole document uses the same font, the Font box will appear blank.