Can a person with dementia revoke POA?

Thank you all for your responses. He wasn't in too bad of shape before entering the hospital. He was still driving and living on his own, taking care of his banking and everything. I only helped when he needed it and he knew when he needed it and just simply asked. He made me POA as soon as he was diagnosed over a year ago. He knew what it was all about and wanted things to easy for me in order to get things done for him. POA was all his idea. His last visit to his nurologist just 2 months ago was great. His Doctors all agreed he was doing fine. I am 2 blocks away if he needs me and between my brother and I, he was checked on once a day. This all took place after his release from the hospital. The withdrawal started as seizures which actually looked like a stroke. we called 911 for him. The problems started after he came home from the hospital. He was to have 24/7 care and we saw to it that he got it. But not with this girl. For whatever reason, this girl just decided to step in and put ideas in his head. He wasn't to drive for 90 days so she took him to her lawyer and had these POA revoke papers drawn up. The med that affected him was xanax. I've been told that the other day his Dr put him on something different when his current script runs out. I've looked in to legal pro bono but so far no luck. I just can't believe a lawyer can do this without looking into it as to why he had a POA to begin with. But on his good days you can't tell there is anything wrong with him. Esp if you don't know him. Thanks again for your feedback!

It would appear he is competent enough to state his decision to a lawyer.
If you were his POA and he landed in the hospital due to lack of medication, I am surprised you were not charged with neglect. As POA it was your responsibility to see the meds were there. Ask a lawyer for an opinon.

Withdrawal - from an overdose? What med was he taking? Apparently he took too much, so the question arises if this occurred while he was living with you (as your profile states).

The second major question is WHO is this woman, and how did she get or become involved with your father?

You state he's "not in his right mind." If you have physicians' statements to this effect, affirming that he's not capable of making legal decisions, you might want to write to the attorney who revoked the POA and advise him of that situation, reminding him that your father wasn't mentally capable to revoke the POA.

Lawyer up, and realize you may need to get guardianship if you do not already have letters of incapacity in hand. This is a classic tale and if a person is not legally as well as practically incompetent, yes they can at least try to change a POA. Sorry this has happened to you and your dad, but don't just let it go! You say you cannot afford a layer, but look into pro bono, do whatever it takes, because frankly you can't afford not to, unless it is OK for your Dad to lose every penny he has ever saved and then need your funds or full time caregiving for his needs once she has milked him for all he's worth.

And, if you do not successfully contest it, and he has in fact signed a new POA for her, it will stand. Here's hoping that the prior doc's determination of dementia will be sufficient ammunition. I suppose if you really can't get your own estate planner or legal eagle to help, you could put a copy of that report in the mail with a calm but threatening letter of your own stating that any responsible caretaker should have realized that your father lacked capacity to change his POA, that you have not resigned as POA and have no plans to do so, and that any attempt to interfere with financial matters or use any of your father's funds as POA by a third party will be reported to the police and prosecuted.

So I'm still confused about where "the girl" came from. Was she one of his caregivers? An old girlfriend? How did she insinuate herself into his life?

Sounds like a typical gold-digger - they come out of the woodwork - I wonder if she has done it before?