I ran a half marathon and feel good but after my knee started to hurt so bad i can't even walk but it is not inflamated ?

RICE= Rest,Ice,Comp-: Ression with a ace wrap, & elevate, to allow things to settle down for the next 3-5 days. Nsaids like Ibuprofen or aleve (naproxen) for pain & discomfort would be helpful. Overuse of a joint can cause inflammation of the lining of the joint (synovitis) which can cause the symptoms you are having. Should feel better in a couple of weeks, if not seek an orthopod's advise.