Why does the page number on page 3 restart at 1?

When I add page number to a header (I’ve done this many times successfully), the first page is numbered 1, the second page is numbered 2, and then the numbering restarts on the 3rd page at 1 and is sequential to the end of the document. How can I make it sequential from the beginning?

It sounds as if your first and second pages have adopted different page styles.
To examine your page styles, click on the ‘Styles and Formatting’ menu button, or press ‘F11’.
Try applying the same page style to your 1st and second page as your 3rd or 4th page. You may also have to double click on the page number and choose an offset.

Note: potential duplicate of (http://ubuntuforums.org/showthread.php?t=2007378).

Another possibility to the one mentioned before;

you have a page break with a page number reset. It is a bit nasty to find out, because you do not have to apply a new style. In other words, the style can be the same, only the numbering is being resetted.