If you can't reach your site, first make sure you have a connection to the internet and you can browse other sites.
Use an online ping or trace route tool to check if your site is online, http://www.dnsstuff.com offers a number of tools for that purpose
If you can reach the server from a different location, there's a possibility that your IP address was blocked by the server firewall for number of reasons including login failures, denial of service attacks, etc... or there might be a routing issue in the way between you and the server. In this case you can open a ticket and our support staff will be able to restore your access, for routing issues please provide a traceroute and ping results from your PC.
If everything else failed and your site doesn't seem to be responding to a ping or trace route. Feel free to submit a support ticket and let us know what steps you took that indicate a server outage.