The only thing i can think of right now is if a book/addin, that opens before
the Personal, sets the Application.EnableEvents to False. In that case, the
_Open of the personal wouldn't run. Such a property would be set through
code in one of these open addins/books. However, still, there some code that
closes the personal book, and you 've already looked into that and found
nothing.
The book could also be corrupted. Try to remove the book. create a new blank
one with just the Workbook_Open and a msgbox. Try this new one. Also try with
another name. Finally, if it work: Open the personal book and a blank book,
and in the vba ide, drag the code modules to the new book. Rename and save.

There is probably be some other explanation, but i don't see any right now.
Maybe someelse will have a better idea.

Regards,
Sebastien