A family of Microsoft word processing software products for creating web, email, and print documents.
You've either got a virus, a bad add-in, or a macro in your Normal template that's bad.
Get yourself some virsus scan software. This one is reportedly good and it's free for non commerical use. http://www.sophos.com/en-us/ I use Norton and it's very good.
Restart your system and then when you go to start Word, hold down the shift key and this will disable all add-ins. Check if that corrects the problem. If it does, look in Word's startup folder for any add-ins and disable them one at a time until you find which one is causing the problem and get rid of it.
Also you could try settting up a new user account and see if that clears the problem. If it does, it could be a problem in your Normal template with a macro. Do you have any in there that you know of?
Hope this helps