Hi,We are using BSNL Broad Band Connection. Last couple of weeks we cannot acces yahoo and its related sites?

Hi,Its for my friend.They are using BSNL Broad Band Connection. Last couple of weeks they cannot acces yahoo and its related sites.We are using very same connection. But we easily access the same. They are usinf ISA 2004 for control net usage. But they didnt blocked yahoo sites. Plz hel me to rectify the problem...