A very common claim made to any web host is "My site is down!" But quite often this is not actually the case and it isn't the hosting server that is down! (especially with reliable hosting providers like Hosting Australia!) It can be a localised issue to your PC. Internet Service Provider (ISP) or perhaps the hosting server firewall has placed a block against your IP address, preventing access to your site.
A great way to check this is via a handy site "Down For Everyone or Just Me" (http://downforeveryoneorjustme.com/). Simply go to the page, enter your sites URL and hit enter or click the "or just me link". You will instantly get a status of your website, up or down.
A very handy tool to discover if you need to contact your Web Host, ISP or IT provider.