Sounds like someone has restrictions for access set up in their router.
Check the manual, and see the person with the router password, to confirm or
deny this.

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>A friend has a wireless connection to a router, then through an ADSL mmodem
> to the Internet. His internet works well until about 7pm when there is
[quoted text clipped - 4 lines]
> access?
> The PC uses only the Windows Firewall with no 3rd party one.