This is usually caused by a corrupted normal.dot file, which is Word's default template. A reinstallation/repair of Word does not re-create the file.
Make sure Windows is showing file extensions. If not, go to Folder Options, View tab, and untick "Hide file extensions for known file types". Click OK.
Make sure that Word is closed.
Then Search on your computer for the file normal.dot.
Rename it to normal.old.
Start Word to see if it opens correctly.