Once you change the nameservers with your domain's registrar, it takes several hours to several days to fully propagate. Do not cancel your web site with the old host until this period is complete. Usually the transfer is quick and seamless....but.... once in a while... !
Across the world is the Domain Name System (DNS) that directs all web traffic. They translate a domain name into the IP address associated with the site you are seeking to display on the host server. When you change your nameservers at the registrar, these changes are sent out across the DNS, telling them of the change. Across the world this may take as much as 48-72 hours, altho it is usually much much faster. Click HERE for a fascinating 6 page article on how it all works.
Interesting to note, it is also possible the area served by one DNS server will refresh quickly and display your new info, while the adjoining area's DNS may take a day or two to refresh. So you could be talking with a customer by phone who is still seeing the old server while you are looking at the new one. It happens!
Happily, most domains propagate within a few hours, and once in a while within minutes.
If you would like to see the route you take between your computer and AmeriWeb's Canada Server click this link:
To access our server in Canada, our office computer bounces from the Chicago suburbs through an ATT hub located in Romeoville, travels through Wichita and goes on to Montreal. Later today, it may take another route. On occasion our office routes through Europe before returning back to our hemisphere. That is the magic of the internet, the most efficient route is always used even if it is geographically more distant.