How can you get power attorney from incompetent father?

If you mean that he is incapacitated to the point where he is mentally incompetent to know what he is doing in signing a power of attorney, you cannot. If he cannot comprehend the nature of his actions, then he cannot lawfully execute a POA. IN order to get control over his affairs at that point, you will have to have him declared incapacitated or incompetent and be appointed his guardian.