Anyone can use magic. If magic isn't working for you perhaps it's because you have doubts about it working. I didn't have to unlock any powers within myself, I simply did it and it worked. I advise working with something small.
The way to 'unlock' the magic within, as you put it, is to have a frequent routine to practice magic. I don't mean casting spells; spells are not magic. They are but a tool. By a practice, I mean meditation, research, visualization, frequent rituals to banish your home of negative energies, introspection (know thy self!), and more of similar.
Magic, you see, is not some special ability. It is affecting change that you want to happen. It may be internal change, which many believe is the most important. But the change can also be external.
There are some possible reasons your attempts have not worked.
Firstly, you are inexperienced. If you don't know what you are doing, results may be more difficult to achieve. So again, establish a practice. Be ever the student. And, as people on the internet say, "get good."
Secondly, your desired results may not have been realistic, or maybe not feasible at this juncture in your life.
You may also be seeking immediate results with something which takes time.
There are so many possible reasons. You did not say what you were trying to accomplish, so nobody can offer advice along those lines.