Moving Randomly

I have a creature that is moving randomly. When there is a collision it changes the direction, but after that it disappears. Can somebody tell me why and how can i fix this?
There is the code: http://www.codesend.com/view/54587302b7155066bfd8caac1c3ffa68/

Check out Unity Steer:

http://www.arges-systems.com/articles/35/unitysteer-steering-components-for-unity/

http://www.google.com/search?hl=en&client=opera&hs=5jX&pwst=1&rls=en&channel=suggest&sa=X&ei=Pd6dTYbhLqGE0QGJ0rG1BA&ved=0CBQQvwUoAQ&q=unitysteer&spell=1

Will help =).