Issue: duplicate text areas

Hello,
I have a problem with Word (I'm not sure which version it is, it's on my desktop computer. I'd say it's Windows 2000), and I hope you can help me please. Forgive me in advance, but I think it will be confusing...
When I try to insert a text box in my Word document, it inserts it in duplicate. My text is therefore written twice, and if I try to delete one of the boxes, both get deleted. Furthermore, if I want to place a new text box elsewhere in my document, the text from the first text box appears and I can't insert my new text without modifying the first text. In fact, I have the impression that all my text boxes are "linked" and that if I change one, I change them all. I'm not sure if I'm clear. If anyone understood ;-) and can help me, I would be extremely grateful!
Thank you very much in advance to everyone who reads this message.