Knee pain , grinding sensation , locking and cracking some times gives way , if i put my hand on it i can feel it grinding worse in the cold. any idea?

Many possibilities: Could be some arthritis (though you are young), a meniscal tear, scar tissue, or a loose body. Some people just have crackling knees without anything serious wrong with the knee. It really depends on many things...Did you have surgery before, or a major injury? It sound like you should see a sports doctor to at least have an exam and xrays.

Knee cap.: It could be some wear on the kneecap and you could have maltracking of the kneecap. See a non-surgical sportsmedicine specialist, who should be able to diagnose this and provide treatment.