Web Site Accessibility

I am having a strange problem - at times I am not able to see my website on my computer or on any office computer. I get calls from clients that say they can not see it either. My webmaster shows me a report with no down time on the server. I believe that because I can see the website on my phone's browser and also have called friends that can see it when I cannot… Is there any insight anyone has on the subject? Any information would be greatly appreciated

 

two examples - but it is sporadic - doesn't happen all the time
http://cscslc.org
http://eyeneeds.com