Outlook Express 6 won't receive email messages at start up

I just bought a new Dell computer with Windows XP that had Outlook Express 6
loaded on it. I have checked off the button to have Outlook check for new
messages at start up, but it doesn't do it. And once I am on Outlook, I have
to push the Send and Receive button many times before it will start to
receive messages. And it seems that even then it doesn't get them all.
Sometimes if I push the button again, even more messages appear. I had
Outlook Express on my old Windows ME computer and never had any trouble with
receiving messages so I don't think it is a problem with my email address.
Does anyone know of any updates or patches that I can download to correct
this problem? Any help would be appreciated, since I don't really understand
all the technical aspects of my computer. Thanks!