Make sure that "Hide spelling errors in this document is not checked." Then,
select the entire document and go to Tools | Language | Set Language and
make sure that the appropriate language is selected and that "Do not check
spelling or grammar" is not checked. Turn off language auto detection, which
can cause problems.
If you find that "Do not check spelling or grammar" is enabled for some
paragraphs, it may be that some of the styles have that language setting. It
can be quite baffling how this can happen. I was working yesterday in a
document based on a template I use frequently. I noticed that misspelled
words were not being marked. To make a long story short, I found that
several of the styles in the document had become formatted as "Do not check
spelling or grammar." Yet when I went to correct this in the template, I
found that they were correct there. Just another one of those Word
mysteries!
