This did the trick, with no need to turn off the firewall....
I managed to change it manually but used the alternate configuration tab in the IPv4 properties in case I want to change to any house connection the automatic IP will act and when changing to the N900 connection it will also connect but waiting not more than 2 minutes (due to the IPv4 will run the automatic first and after finding a no successful connection it will check the alternate configuration)

Thanks 9000 for all your help and time spent due to my problem