To help gain more insight into your problem, I recommend liberally sprinkling Debug.Log() statements through your code to display information in realtime.
Doing this should help you answer these types of questions:
- is this code even running? which parts are running? how often does it run?
- what are the values of the variables involved? Are they initialized?
Knowing this information will help you reason about the behavior you are seeing.
How to report your problem productively in the Unity3D forums:
When you post code, please use code tags: Using code tags properly