I fell on the stair case sraight on my back i felt my back crack since then i have a burning sensation on my left side and can't hardly walk ?

Go see your doc!: Back injuries leading to change in sensation and inability to walk need to be evaluated. Go see your doc for a complete evaluation. Go to the emergency department if you can't control your bladder or can't walk due to muscle weakness, not just pain. Numbness in your crotch area is also a really bad sign and needs to be evaluated emergently.

Need attention: You need some imaging like xray burning pain is mostly due to nerve problem, like pinch nerve. Please see your doctor.