If it's the same for other networks, then let's drop talk about yours and list a few others that aren't working-- show both the connecting to and refused messages for a few different networks. That helps us to know what servers and ports to check into.
As far as you MAC address, that is unlikely the problem. If you can connect at all (that includes web browsing), then your MAC address settings should be correct. If anything, you are blocking a port or set of ports through a router or firewall even though you normally don't need to forward any ports to connect.
