During the 20th century, the subconscious mind of many people were opened up by various practitioners and teachers. Sigmund Freud, Carl Jung, William James, Edgar Cayce and Ron Hubbard were a few researchers into this field. These men were modern day Prometheuses who were not content to follow the academic experts of their time.
This is too big a subject to put into a blog entry or even one book.
Past life memory is also hard to face because it's full of painful deaths, horrible loses and incredible setbacks. Just look at mankind's suffering by war, disease and famine.
I believe it's possible to recover past life memories and to learn from them. Please check out "The Memory Recovery Project" on the right hand side of this page and other related blog entries.