How do I motivate myself from a broken PhD. effort?

I have always had that one dream and that is to be a research faculty at an university. I did my undergrad and masters from top-notch places and I was doing my PhD. in one of the highest ranked places in the US. But somehow my interests never matched the faculty interests and I eventually gave up.

Now at the age of 27 I am trying to restart my journey from scratch in a different department in another subject which always fascinated me. Took up the highest courses there and trying to fight my way in from nowhere. But this transitional situation makes my funding uncertain.

I feel a deep sinking feeling about my lost last ~5 years of my life, the masters and my initial PhD. effort. My peers have gone far ahead in the meantime. I feel very depressed at a very deep level.