Check your Word Startup folder for unwanted templates. In Word, click on Tools | Options | File Locations, select Startup from the list, then click Modify to get the full path of your Startup folder. When you've noted (or copied to the clipboard) the path, hit Cancel (you don't want to modify your Startup folder) and close down Word.
Now, using Explorer, navigate to your Startup folder and check what template (.DOT) files you have in there. You may spot the offending file straight away, or you may need to remove all the .DOT files to a spare directory; restart Word with no templates running on startup; then, one by one, add the templates back into your Startup folder (restarting Word each time) until you find out which file is giving you problems. Remove it from the Startup folder.
I'd also strongly recommend sweeping your PC with an up-to-date virus checker.