Falling through the floor after jumping off the second part of the slide

I managed to beat the game. I had to exchange my original copy for a new one. Once i completed it, i tried starting a new file one Jedi Grand Master and it would not let me get passed the train in the very beginning of the game. Game sounds like its over working my system, and spite how long i leave the game in a single spot to "load" it will not let me past.. I am on Zeffo on my Completed story and i keep falling when i try and slid down the ice ramp going to Venator Wreckage.. Please fix this.