404 Not Found error usually is rising up when the requested URL is not found. Let's review the most common situations:
First possible reason why your browser throws Not Found error is the domain's DNS zone misconfiguration either on registrar or on server side. Using DNS tools try to find out if NameServer settings are properly set for your domain. \
Now use DNS Lookup tool and check NS in drop-down menu:
If you can see your domain's NS settings link on the picture below, then DNS zone is properly configured and you should search for another solution.
If the result page shows another information, like:
please press on "Click Here" link and you will see the result of your DNS request in details. Now if you see that your domain's DNS zone is not cached on the root DNS servers, like on the picture below:
then your domain is not registered or no NS records are set for it. So you should either register it, or contact your registrar and ask them to set valid NS records for your domain (you may find our NS records in your account activation e-mail).
Otherwise, if you have clicked on "Click here" and you see the following page:
Then your domain DNS zone is misconfigured on the server side. In this case you should get in touch with our support team by opening a trouble ticket or sending an e-mail. They will make all necessary changes to fix the issue.