Have you tried clearing Safari's cache? This may be a problem with corrupted cache and not the browser or the site themselves.
With browser issues:
Always check to see if other websites are problematic.
If they are, then it's probably your router, firewall, or connection to the outside that needs to be fixed.
IF it's not, and it's site specific, check to see if another browser can access it. 9 times out of 10, if it can, it's a cache issue.