Sounds like your not connecting to the internet. If you
have dial up service, make your connection to the
internet and then press send again. Messages will remain
in you Outbox until you connect to your internet service
provider.
I am having same problem with Outlook 2003. I am connected and it just
won't send email. Everything else works great. I have run scanpst and
there were some problems, but it says it repaired them.