Website down issues are common due to some unknown server errors in hosting. Problems are so many, you can easily know your site is accessible in worldwide or not with Cloud Monitor.
Cloud Monitor is a web based service that pings your website using their different monitoring stations worldwide. It also shows how much percentage of packets are lost in different locations of the world. It is very useful service every blogger/site owner, to know which country blocking the site, how much packets are lost and where the site is down at present.