Open it from windows explorer, not word or notepad.
In your start menu, find 'my documents' and open it. From here, right click your document and choose 'open with' and then choose notepad.
(By the way, you should reply to the others in the same thread so that everyone can see the whole conversation in one place)
Open Word with a blank document and select Insert >text from file and select the file you can't open. I think the file may have a corrupted header. Failing that, if the document isn't confidential, you can send it to me and I will try my best to fix it and return it to you.