You may experience cases where you can view other websites, but not your own. Other services related to your domain name may also be affected, such as FTP and email. First, check that your ISP or LAN is up and running. Second, verify that your website's server is up and running, preferrably by using another ISP to access the Internet.
Assuming that there is no problem on your end and on the server where your site is hosted, then this could be an issue with one of the "hops" that your ISP uses to access the site being visited.
The Internet is not one homogenous line from your computer to the website server. ISPs usually use other ISP's network infrastructure in order to pass the signal request. For example, if the website server is located in California, from the Philippines, the signal is routed first to Taiwan, then Japan, then Alaska and only then to California. So if there is a telco problem in Japan, then you won't be able to see the site in California even if there's no technical problem on your end or the server end. Unfortunately, this situation is already beyond the control of your ISP or your hosting provider. The next best thing your ISP can do would be to switch to a back up pathway, if they have such an arrangement ready.
An easy way to determine any issues in the hops is through the tracert command. This is typed in the command prompt window (Start > Programs > Accessories > Command Prompt):
tracert (IP address)
For example:
tracert 69.93.219.154
This will list down the different signal hops starting from your computer all the way to the target server. Any portion where there is a time out will indicate a problem in that particular hop.