Cheerleaders, I need your help!!?

I had a wonderful lib, and just in the past 3 weeks i have totally lost it. I can not hit it anymore. I think the problem is with my knee. I can't keep it locked. I work out everyday, and i have strong leg muscles. but i just can't seem to hit it anymore. Every time we try it, and i don't get it i get more and more frustrated ( i usually end up crying ). So i need some help, please. I want to be able to execute it again. I have even done an arabesque. HELP ME PLEASE!!!!!!!!!!!