Problems loading certain websites

I am having a problem loading several websites that I know are hosted on the same server. Three of these sites I have created. I am not able to load them using my iMac, iPad, or iPhone. The browser I am using is Safari and Mobile Safari. This issue has started suddenly. If I turn wi-fi off on my iPhone, I am able to load the sites thru the cellular connection. This makes me think the culprit is either my cable modem or my AirPort Extreme. I have had friends visit the sites with no issues.

The sites I am having problems with are...

www.hbsouthprinting.com

www.kleinscuba.com

www.parkbaptistchurch.org

www.mgmoptics.net

Any suggestions is greatly appreciated.

Thanks,

Marlin