ya, sounds like u installed a "NO CD" crack for it, via a "Diablo II.exe" file, if ya did do that, jus replace it with the orig. .exe file. using the update might not work, chances are your gonna need a friend to send it too you or your gonna need to reinstall it again.
This is why we allways remind you:
BACK YOUR FILES UP BEFORE YOU DECIDE TO MODIFY THEM!!!