I have serious self belief issues and a negative mindset I can’t escape?

I’ve always dreamed of becoming a successful musician. Always. I look up to various artists in the industry in a very emotional and inspirational way. It’s my only life goal to fulfil my biggest dream. I have an unhealthy obsession with doubting myself and telling myself it’s impossible to make it and it’s never going to happen. I also feel extremely negative towards all situations I’m involved in. I’ve allowed myself and my dreams to be engulfed by this disbelief in myself. I haven’t told a single person about this dream, ever. No one knows about it. I don’t know where to start trying to pursue it. I have no ties with anyone who could help, hence why in my head I’ve made it seem impossible. Is there any way I can adapt to a more positive, hopeful and optimistic mindset rather than constantly putting myself down? I know I’m in control of my mindset but I’ve made so, so many attempts to change and nothing has ever worked out for me. This is my last resort