Problems accessing emails

this is a strange problem.Whenever i logon to mail.yahoo.com to access my emails and after i fill the required details i get a message "login.yahoo.com could not be found" and this same for gmail. this problem is also faced by one of my friends who has UBUNTU 64 bit installed, but another friend of mine doesn't face any problems like this.

When i first installed UBUNTU 5.10 on my system i faced this problem.since i couldnt rectify it i reinstalled it again.After that everything went fine and i could access my emails but from yesterday this problem has started to trouble me again.

please help me out so that i can also help my friends. thanks

Hello! Are you able to serve on the internet? Jorn

i can easily surf on the net and download any files i need but the problem is only with yahoo,gmail,hotmail etc. recently a friend of my accessed his mail on ebiz.com and he could that easily.

when i reinstalled UBUNTU i could access my email on firefox but not on opera.also at that time while being a root user i couldnt access even in firefox.

help me out please.this problem is pulling my brains out.