free space on it, but assuming that is not the problem, try deleting all instances of "Normal.dot" on your hard drive, (Start > Search (for files and folders), Normal.dot).

Normal.dot is the main template for all Word documents, and can get corrupted. If you delete Normal.dot from your computer then re-open Word it will create a fresh version of Normal.dot.

This may not be the solution, but it is a place to start.

Mark