You don't say how you are retrieving mail. If you are using an email program in conjunction with an ISP's POP3 server, check that you have configured the program in all computers to leave messages on the server. Also check that, in the Laptop that isn't retrieving the messages, they haven't been filtered as 'spam'.
If you want to have all of your mail available in multiple computers, I'd suggest using IMAP rather than POP3 protocol. With IMAP, all mail remains on the ISP's server and your email programs "synchronise" with the server.