I cannot use Yahoo search or get to www.google.com at all

Hi,
I have been having this issue where I cannot use the Yahoo search feature or get to any google sites at all. I can use Yahoo mail and search within yahoo sites except the home page.
I read some answers from other people having this issue and tried to check my hosts file at system32\drivers\etc. but there is no hosts file there. Searches for the hosts file on the computer find nothing! What is happening here and where could it be?

I run Windows 7. I have also run a couple different malware scans which found nothing related to this issue. Could there be some other reason why I wouldn't be able to use these certain websites?

Any info would be great
Thanks!

Sarah