A family of Microsoft word processing software products for creating web, email, and print documents.
On the Page Layout tab, click Columns, then More Columns... Select the preset picture for One (even if 1 column is already selected) and click OK.
If this is just a problem with a single document, and this fixes it, then you're home free. If this is a problem with all documents (and this fixes it), then you'll need to make the change in Normal.dotm (though I think it unlikely that this could be a problem affecting Word 2007--it's more likely to crop up in a legacy document).