Car wont start

First off, you should check to see if your battery is charged, getting a charge, and holding a charge. New batteries can be faulty. The fact your generator light comes on says it is not charging. Too low an idle will bring that light on as well.
Check the battery clamps. They must be shiny silver clean, not black or corrodded with gunk. Make sure the connections to the posts are tight.
Really, if you havn't touched anything, all should be good.