DNS Expert Needed-Site Loading Problem in different countris

My site [login to view URL] has some problem of Loading in different countries at different times, the reason is un-known to me, specially in india, Bangladesh and other countries as well. some times it loads, and some times it does not loads. the Hosting support says there is no problem on their side. A testing site [login to view URL]://[login to view URL], or [login to view URL] also give the results some times ok some times not. I need an expert opinion and solution, why it happens, and how you can help for solving the problem, and how much you are confident to solve the problem.