It sounds as if you may have the page set-up formatted to start in the middle. Go to Page Layout and open the dialogue box by clicking on the tiny triangle at bottom right of that section of the Ribbon. On the Layout tab, see if Center, rather than Top, is in the Alignment field. It should be Top.

If the problem is actually in your header, turn on you hidden character display (the paragraph marker at top right of Home/Paragraph in the Ribbon), then double-click in the header area of the document to open it, look for and delete any extra paragraphs, check to make sure that the space above and below the remaining paragraph is set to zero, and then, if necessary, set the header depth in the page set-up dialogue you were in before.

Best,
Ulodesk