Isolation Tests
From OCAU Wiki
If you are having problems with your Line you and you call your ISP about this, you will be asked by your ISP to conduct an Isolation Test.
http://whirlpool.net.au/wiki/?tag=Isolation_Test.
basically it means you need to disconnect ALL the devices from the Telephone line and Outlets and then reconnect the Modem and then after succesfull connection you then start plugging in each device one at a time to see which outlet/ device is causing the problem...