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You could try some of the suggestions on this page, it seems like a reasonable place to start:
How to Test Network and Internet Latency (Lag) in Microsoft Windows - wikiHow
You could maybe also...

Can you use traceroute or ping to tell you what's going on with your traffic? If the browser is failing to connect, you must have sufficient connectivity to your ISP's nameservers - and your...

If you're having 'my-site-is-dead' paranoia (happens to us all), websitepulse is pretty handy:
Free Monitoring Test Tools by WebSitePulse

And you could always try a shamefully unattractive, but...

A proxy is what I just was when I followed the link you posted! It works just fine. Did you ever hear of 'proxy voting'? You nominate someone to vote for you. A web proxy (this way is sometimes...

Have you tried using a proxy to check to see if other people on the Internet can see those sites? I usually use Google Translate for this job.