Problem when browsing Internet

Hi guys,

My friend has a PC. He told me he has a problem when opening Iranian pages. The problem was that the browsers couldn't open them. Both of us live in Iran. I told him bring your PC in my office and I try to find out the issue. Our modems are the same and each one of us use TP-Link TD-8817 modem to connect to the Internet using ADSL service. He told me that the issue is to do with the OS so I tried his PC using my modem and my line. His PC didn't has any problem with my line in my office. And I said him the problem is not about the PC, call the ISP. Our ISP is the same and the line we both use is from telephone company. They told him the line hasn't any issue. Now the only point I can think of it is about the updating of modem's firmware. I think probably the issue only remains to the modem so updating it maybe is the answer.
What do you guys think?

Thanks in advance.

OK, I try that way. Thanks for your idea.

No mate. I completely always appreciate your replies weather it can help me or even not!:)

I couldn't configure his modem in quick start mode and should to configure it in bridge mode. And since I don't know how to do that and it's somehow irrelevant to this thread I create a new thread named "how to configure in bridge mode". So anyone who wants help me please goes to that thread and answers. Thanks.