My police fund stays at 0, when I drag the fund selector all the way right it goes back to 0$ (left) after a few seconds.
How can I fix this?
It sounds like the infamous Phantom Slider Bug (http://sc4devotion.com/forums/index.php?topic=9249.msg284513#msg284513). Read this thread for information about the causes and solution.
Unless you are sure which lot is causing the problem, the best solution is to demolish all police stations then save and exit the game. When you re-enter the problem city, you can rebuild your police stations.
I hope this helps!