How does one develop personal power?

I'm struggling lately in all areas of my life. This has been going on forever, really, but I'm looking at the last several months in particular. Feedback is that I fail to take action when action is warranted or when I perceive something as a problem. I realize that this has to do with that I don't feel like I can do anything that will help. I can also recognize where this comes from. I was taught by my parents growing up that I was only a child, and would always be their child, which they owned, and nothing was mine because I owed everything to them, and I could not do anything without their approval, and they did not approve of trying to do anything on my own. Anything that I did try to do was never good enough, and was subject to criticism and discouragement.

My parents never expected me to leave home. They didn't know how to let go. They sabotaged my efforts to choose my college when I was 18, and forced me to move with them to another state. I fought a war, and it took me a year, but I did leave the next year. I broke free, severed ties, and was alone and miserable and dependent on roommates and got married when I wasn't ready, and couldn't see that I had any options. I felt that I couldn't take care of myself and what I wanted out of my life was never a consideration.

Now I am doing so many more things than I did before, but the theme of never being good enough keeps repeating. I am still stuck. T told me that she has never seen treatment be successful with anyone who was determined that they can't change. I want to be able to change, but I am afraid. It seems like it will never be good enough, and I will keep getting stuck. It seems like I don't matter, and nothing that I do will ever make a difference. I often think that I am invisible, and have felt that I had no impact on anybody, and that I should not be visible or have any power or influence anyone.

I want to be confident and capable of living my life effectively and making a difference. I wish that I knew how to be like that. Any ideas?