At one point or another in the book I'm writing, hard lines were placed in the text, all across the document. I want to remove them and can't- help!

These may be paragraph borders inserted by AutoFormat as you Type.
Weird Lines and Borders
If so, you need to select text before or after the line (could be either, but likely before) and turn off paragraph borders.

Thanks for the suggestion, however I neglected to explain that those lines were put in when I was at a writing retreat and we had to make a demarcation of where we were at a particular point. But they won't go away, I can't delete them. Even if I delete the entire paragraph to re-type it, the line still shows after the paragraph is gone!

Turn on display of non-printing formatting marks. (Alt-Shift-8)
Is there a paragraph mark before or after the problem line? Try formatting the borders for each of those paragraphs.

If this is the case, also look at Basic concepts of Microsoft Word: An introduction. I suspect you are using the Enter key to space your paragraphs.