The most likely reason is that the DNS hasn't fully propagated yet. It takes from 24-72 hours for domain name servers' change to propagate throughout the Internet. For some locations your domain will be loading new store faster (in 6 hours) for some it can take up to 72 hours.
Also, please let us know before changing name servers for your domain, if you originally signed up with different domain name. Some changes has to be done to your account before new domain will start working.