This is the Internet; it depends on so many services provided by so many different providers, each using different technologies, equipment, and tools. It is not the place to list all the causes for such problems you are facing; this would require pages and ages.
If other people are able to connect to the site and you are not, this means the site is ok, and the problem is caused by an external factor other than the Site itself.
The most important causes for such connectivity problems come from your computer, or Internet connection hardware, followed by problems related to your Internet Service Provider, and finally Problems resulting from one of the World Servers being in trouble, or international communication lines being disrupted etc. These problems might affect your connection to a certain locations or sites while the other sites remain functioning normally.