Malware problem:Unable to to do searches on Google etc...

Hello,

Having a problem and looking to pick some brains.

Problem:

1) When I open up my browser...it goes directly to my home page
(yahoo). That is fine.

2) If I type a topic in the search field (example: ESPN)...all the pages
for ESPN come up (still fine).

3) When I click on (1) of the pages (for example ESPN's home page)...it
takes me to ads or other search engines.

In this case, I am unable to get to ESPN's pages no matter what I try.
It keeps re-routing me to pages with ads or other misc. search engines.

I ran AVAST and did find one virus but still am having the problem.

Any assistance/advise would be appreciate...

Thanks

Mark