If they are in the Sent Items folder, then OE got confirmation from the
news server that they were accepted.

Any of several things might have happened.

- The news server after initially accepting the post decided to delete
it because it failed to meet news server administrator standards.  This
could be due to language, spam, use of HTML, inclusion of attachments,
to large, to little new text compared to quoted, text, etc.  You would
need to contact the news server administrator for their specifics.

- The news server is actually a bank of news server and they are
out-of-synch.  When you connected a second time you got a different news
server than  when you posted and the post didn't make it there.

- Or the problem could be on your OE or it's settings.
 - Make sure that Tools, Options, Read, Get xx headers is NOT checked
 - Select the Newsgroup and View, Current View and make sure that Show
all message is checked.  The Uncheck Group by conversation.  Then click
on the Sent column heading and look for your message around the time
that you sent it.
 - If you still have problems, Right click the newsgroup and select
Properties, Local File and RESET.  That will mark the newsgroup as if
never visited and download all the message still on the news server when
next visited.

It could also be the news server you are using.  If they are
microsoft.public.* newsgroups, set up an account for this news server:
msnews.microsoft.com
and subscribe to those newsgroups on that news server.