Was it before man, or did they existing during the beginning of man's history?
There are no certain answers, but it looks like dinosaurs were millions of years in the past, and humans were only hundreds of thousands of years in the past.
You can't get straight answers from scientists because when they don't know something, they will not admit they don't know. They would rather be wrong than uncertain. For example, they insist that gravity and air pressure and stuff have never varied, but dinosaurs obviously could not have survived in what we now call normal conditions.