Many times i seen that to some series of IP adderess my site does not open.But opens on Proxy servers. I reported it to my host provider but they said its your ISP problem. Please tell me whose fault is this? If ISP prob then why this happens with my site only?
I would check your DNS health for those sites. Are you able to open the site directly by the IP address, and not by domain name?
Please check it. At present also i am not able to access my site. http://www.astroprayag.com/ http://www.patfs.com/
Both opened up fine for me. I'm having the same issues on my websites as well http://www.h2bots.com is one of them. It's driving me mad! really it makes no sense. EDIT: Just found out what was the problem. I went to www.intodns.com and ran a DNS Health Check as suggested by RHS-Chris found that the nameservers were acting up. I called GoDady to find out what could be done, and apparently the Nameservers they originally gave me we outdated and old nameservers that were known to malfunction. They had me switch the nameservers to 2 newer ones and that fixed the problem. Give that a shot and see if it helps your issue.
Try to use alternative DNS servers like google and opendns on your site, and check if the problem persists.