Replying to My knee hurts

so i have had problems with my knee for years just from hitting it on a ton of stuff when i was younger and i would always hurt the same knee. For the past two years or so now if i do something for to long like ski for multible days my knee starts to hurt like a bitch and i cant put eny pressure on it.some times i will just be walking and i can feel it comeing and I wont be able to walk for the day.i have this right now and i havent been able to go skiing for 2 days so ive just been doin a little rail in my backyard and i really want to ski. I am woundering if enyone else has had this and what i should do to provent this from happening. I did searchbar and it did not explain this.
thx