I hit my knee really hard this morning and when i try to walk i fall from the excrushiating pain. that peice on the front of ur knee is really swolen?

Most likely bleeding: Inside the joint, one contusion please goes and checks it and sees what the problem.

Prepatellar bursitis: Hello you could be having and inflammation or infection if the fluid cushion of the knee cap called preparellar bursitis .... Try some over the counter antiinflammatories like ibuprofen. If you do not have any kidneys issues you can take upto 800mg four times a day . These can be drained under sterile precautions which will provide immediate relief ... If infection antibiotics will be prescribed.