If you're using xl2002+, make sure you turn on autorecovery:
tools|options|save tab.
If you're not using xl2002+, make sure you save often--well, even if you're
using xl2002+, that's a reasonable suggestion.
You may want to consider using Jan Karel Pieterse's addin called AutoSafe (note
spelling).
It doesn't overwrite the existing workbook when it saves. It saves to a user
selectable folder. And when it's done, it either deletes these backups (or puts
them in the recycle bin). And the user can always restore the backups from the
recycle bin.
http://www.jkp-ads.com/Download.htm
(look for AutoSafe.zip, not autosafeVBE.zip, for your purposes.)
Jan Karel's version will know if there was a crash and prompt you to open the
last version it saved.
