On my home ISP i seem to have an issue connecting,
It says connected, But is not showing in the connection bit above the bit that shows the wireless networks. I am running Windows 7 (just incase you are wondering what i am talking about)
Does your router/modem have a firewall running on it? If so, then the Windows Firewall may be interfering. In that case, you will have to turn one of the firewalls off.
Go into the network and sharing center and click on the left hand side where it says "manage wireless connections" Remove the existing wireless profile for the one you are having issues connecting to and reset up the connection. Sometimes the wireless profile just gets corrupt and you have to reset it up.