If Word is really capitalizing at the beginning of each new line, then you
must be giving it some reason to believe that the beginning of each line is
the beginning of a sentence. Are you pressing Enter at the end of each line?
If so, you are creating a new paragraph, and Word (semi-logically) assumes
that the beginning of a paragraph is the beginning of a sentence. If your
text is continuous, don't press Enter; just let Word wrap the text
naturally. If you need a new line (as in typing poetry), use a line break
(Shift+Enter) instead of a paragraph break.
For specific situations where you need to begin paragraphs with lowercase,
you can turn off this AutoCorrect action temporarily. I have to do this when
I'm typing dictionary entries, where the first word in each paragraph is the
defined term (not capitalized). You then just have to be a bit more vigilant
about making sure that you press Shift at the beginning of each real
sentence.
