Debug the code

I have the program where the point in the code is traveling inside the 3d area. The traveling limit is defined by some Z value. At the beginning the point is not going outside traveling limits, but after some time it goes behind the limit and the code in stuck in endless loop. I know which variable is acting wrongly and will give you details. You need to investigate the reason and give me repair solution. Maybe, some other variables are not correctly defined or maybe here is a memory leak. The program is running on custom assembled board with stm32f4 microcontroler, c programing language. I use Keil Uvison IDE. So idealy, you need to have board with stm microcontroller to run the code and debug. The code has around 500 lines in the problematic sketch.