If you are not able to see your website, there could be other reasons instead of server down. There are so many methods to check that your website is up of not. I am here showing few of them:
1. Use a proxy service provider for example use http://proxy.org/ or http://sitesurf.net/ and try opening your website via their form.
2. The step above will visit your website via an external IP address, so you can see your website by using a different computer that is placed on another network.
You may also use website tool like http://downforeveryone.com/ to checks for status of your websites.
If this website tool shows that the website is UP, while you are unable to brows your site, you need to contact your Internet Service Provider immediately and explain the problem to them. The persons at your ISP should be able to assist you.