In Word, Help/Detect and Repair.
If that doesn't work it is possible that the default document template has become corrupt. Quit Word. Search for NORMAL.DOT - you will need to turn on "Search hidden files and folders" under "More advanced options" in Search.
You may find more than one NORMAL.DOT - rename them all to ABNORMAL.DOT
Start Word - it will recreate a new NORMAL.DOT
If that doesn't work, rename ABNORMAL.DOT back to NORMAL.DOT and post back.