Here is a nice PBS page about what happened to the dinosaurs
You could also get lost for a long time following links about dinosaurs in Wikipedia.
Here is a 2013 article from National Geographic about "What Killed the Dinosaurs: New Ideas About the Wipeout"
This article says that apparently there may have been some large volcanic eruptions in India that were causing climate change and that this was already making it hard for the dinosaurs to survive. Then when the asteroid struck the Yucatán Peninsula, it was the final straw for the dinosaurs.
(the Nat Geo article is a report on a journal article in Science: http://www.sciencemag.org/content/339/6120/684.abstract