Unable to brwose with Yahoo and MSN.

On 10/4/03 I could not use the Yahoo or MSN browser. No matter what word I enterered in the search the web box, I always get that the page can not be found.
I was able to do it before that day. I checked for viruses and worms, but I can not still use them. I tried with different systems and they work fine.
Please Help me.
Thanks.