You may ascertain if the website is prohibited by
You are connected to the internet, your access to applications and web are working as normal.
You get the 404 error when a website is inaccessible and you are able to access all other websites.
To eliminate the probability that the website you are trying to access may be temporarily down/ inaccessible; do try again later and if the website is still inaccessible, then it may be probably blocked.