Hi Venny173. Welcome to allnurses.
You didn't say where you are from, but I would advise writing to the various schools
nearby and asking for brochures or catalogs.
Most of the time (in the USA) they will require at least the SAT with a good score. Many also require a Nursing Entrance Exam.
You said the medical assistant certificate didn't work out. May I ask why? Is it something to do with the kind of work?
There are several entry levels for RN. Do a search here under school, or ADN or BSN. There have been many lively discussions about this very topic.
Again welcome. Ask away. We'll try to help.