The previous questions' background being the following:
Since your mate can connect, and you can not, the reason for that must lie in some subtle difference between yours and his setup, which is exactly what we are trying to find out. It may thus be:
- the physical connection, i.e. differences in the way you connect to the upstream router
- settings upstream (i.e. router settings like dhcp leases, port forwarding settings)
- settings on your computer (i.e. everything that can be configured in the network connection settings dialog)
If you could search for every oh so small difference in those points, and try to get your setup as close as possible to that of your mate (aside from using the same ip address obviously), it should, according to therory and our beliefs, work.