From what you say, the problem is with the document itself, not Word, or your network environment.
When something similar has happened to me, Word freezing in a long document, the problem has been a table. The table looks alright, but there is something in it that stops Word.
Have you tried copying the whole document to a new blank Word document, (use copy and paste not insert file).
If that doesn't work, you could try deleting tables from the new copy of the document.
One symptom I experienced was that the faulty table would not accept any formatting changes. Changing text alignment for example, in a cell in the faulty table wouldn't change the alignment.