Troubleshooting OWA 2003

I have a user who is having problems sending mail on one computer. He can receive mail and delete mail, but he cannot send mail. His permissions are set correctly and when he signs on another computer he can access everything and send mail, but when he tries to do it on this one computer, it doesn’t pop up with the New Message box. He can’t send, forward, or reply to mail at all. He clicks on the button and it does nothing. Nothing comes up. No errors or anything. If anyone could help out, that’d be great.