It's hard to say much when you haven't written more about the situation.
Did those links work yesterday? Does it happen to all quizzes and file links? Has anything been changed on the
server recently?
In General
It's usually best to begin in
Moodle Docs, and if you don't find an answer there check with the Forums.
When you make a forum post it is important to describe as concretely as possible:
* what you want to do
* what you have done
* what possible error messages you have gotten and/or a screenshot of what it looked like
* what you are using: moodle version, server type, operating system (Xp, Vista, Mac, Linux), which browser and version you are using.
This will greatly improve you chances of getting a useful answer.
Don't give up!
If you get a useful answer, especially one that solved the problem, mark that one as "useful".