I torn my hamstring (undiagnosed by md) in highschool after a 40 yard sprint. couldnt walk, and my right hamstring was purple. this was 2008 summer. i still can explode or making sudden explosive movements as i feel the pain of it. didnt heal right?

Yes, you may have the sequelae of a severe hamstring injury (grade 3, a complete tear) which did not heal perfectly.

Injuring a muscle without proper physical therapy Will put you in a vicious circle. Proper rehab is required. Stretching and strengthening of the muscle fibers are important in rehabilitating a torn muscle. Without proper rehabilitation you’ll be in a vicious circle. See a physical therapist