can’t open web site.

I have my own web site which I cannot get into. I have tried to open web site, also the webmail account, but cannot enter anywhere.

Anything related to my domain is not working. If my computer is used on a friends router, I have no problem getting in, but when I try on the system which I am using, a broadband and telephone radio system, as I don’t have a telephone line, I cannot get into anything relating to my domain name. Any other web site or webmail is no problem. I am totally confused.

Is there any setting that I should change in IE?

I am using Windows XP Prof. and IE7. Antivirus is NOD32 and Spybot. This is all the protection I have.