Link issue

Everytime i click on a link to be directed to an outside source, it gives me a open window that is blank. Even adscome up as blank open windows. How do i fix it so that i can click on links again, and see those annoying ads? Our computer previously crashed, and my father played with it, further maessing it up. We had to reinstall windows xp professionals over old one and satrt over, but when we put in the interne explorer again, the links were faulty. how can i fix it?