James: Playing around the F/R options would fix a 'Not responding' state, as reported by the OP; all they'll do is affect whether Word finds whatever you're after.

Of course, on a very large document it might take a few moments for Word to return to a ready state after a F/R. Assuming that's not the case, or at least that the problem isn't limited to such documents, a repair (via Programs & Features > Microsoft Office > Change in the Windows Control Panel) is a good place to start.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]