Ok, this has nothing to do with the site itself. This is always an issue with one of the following:
Computer
Browser
Firewall (hardware or software)
Router
ISP
There are a ton of things that could be causing this. If you're able to access the site from another computer then the site itself is up and operational. if it is only on one computer or multiple computers from the same location then it could be that location doing the blocking.
You can try clearing your cache, clearing your dns, checking your firewall, router, ISP, etc.
Not being a dick about this but you need to try some troubleshooting and list what you've done and what the results were with what you've tried.
Try this
link as a start, then the two links at the bottom of the page could possibly provide more solutions.