A family of Microsoft word processing software products for creating web, email, and print documents.
Is this the kind of blank area and dotted line you mean?
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If so, that's the "header" area. The dotted line appears only when the header pane is activated (usually by double-clicking in the blank area), and other clues are the appearance of the "Header" tag at the left end of the line and the "Header & Footer" ribbon. You can click the Close Header and Footer button on that ribbon to put the cursor back into the body text.
You can change the measurement in the "Header From Top" box in the Header & Footer ribbon, or in the Page Setup dialog that you can open from the Layout ribbon. The height of the blank area is always the larger of the "Header From Top" (plus any text you add to the header) or the top margin set in the page layout.
If the blank area you see is not a header, it may be caused by an "invisible" graphic included in your Normal.dotm template. For help with that, see http://wordfaqs.ssbarnhill.com/InvisibleGraphics.htm . Another article that may help is http://wordfaqs.ssbarnhill.com/TroublesomeLines.htm#Borders .