test messages work - but cannot receive e-mail

Outlook 2003 SP2. I am just at the end of a 'recovery' of my PC after
reinstalling all original software plus updates.

I have three pop3 accounts. The "test account" works in each pop3 account. I
could send and receive earlier tonight when I first installed Outlook... but
then it stopped working when I added the extra two accounts and added 400MB
of my old e-mails the new inbox and other folders.

The error says "Task mypop3server.com - Receiving reported error
(0x800CCC92): Your e-mail server rejected your login. Verify user name and
password in your account properties. The server responded: ERR Username/
password mismatch"

It works from my other computers, so it is something with this computer. I
know the username and password is correct - becuase I use the same username/
pssword to log into SMTP and that works fine.

I do not have an anti-virus program installed yet (tomorrow)... but the
windows firewall is in place.

Any suggestions?