It sounds like you've managed accidentally to save the random test input in the default template - so every time Word opens a new document based on the template you get the same stuff.
Best thing is to press F1 (or open up Help) and search for "edit template" and follow the instructions.
In most versions of Word that I've used, it'll go something along these lines:-
1. File -> New, which should bring up a dialog box with a selection of templates. (Office XP has a sidebar which lists types of templates you can choose, "General Templates" bringing up that dialog box.)
2. Right click on whatever looks like the default template ("Blank Document", for example) and open it.
3. Edit it to delete the random characters and then save it.