Hi, just out of interest.
You say "Private Server" is this something your brother is hosting on directly his machine or do you have a separate server at home?
If he is hosting it locally, can he connect or does he have the same problem?? If he can connect correctly then I suspect that it is a firewall issue or anti virus. Check the server.properties and the port has not be changed and that this matches his firewall configuration.
In addition to this, Win 7 firewall has several different profiles. Switching the firewall profile can cause a lockout issue.
Find the firewall rule for minecraft and ensure it works as follows.
Start -> Control Panel -> Windows Firewall -> Advanced Settings -> Inbound Rules
If in doubt you can temporary disable his firewall internally just to see if that's the issue. If you can connect with it off you have found the problem.
P.S. Looking around the forum, there are some connection related issues with logins. I don't know if this is related.
