Mental problem presupposses there is a solution.
That their mental state is not engaging with the world in an effective way. Such as milking a cow to achieve world peace without stating why; more milk in the world, for people to drink to keep hydrated to stay clam to avoid violence and therein war.
Mental disorders presuppose a set of acceptable or 'right' states of mentality. They have a disorder when their interactions with the world result in pain or suffering of other such 'bad' things that society wishes to avoid, that individuals often do not consent to.
I judge someone 'mental' when their behaviour changes radically (over time and instantly) and it does not change back and can not change back. When their way of being is a problem to them. I equate genius with insanity; both depart from the 'normal' and status quo with the line differing over the outcome. A genius impacts upon the world in a beneficial way, while a 'crazy person' impacts in an unbeneficial way. Though this is customisable to the specific case.
When a person gives absolutely everything away to charity, they could well be called crazy. But bear in mind they are also extremely altruistic as well. Crazy and Genius are just two sides of the Quantum dodecahedron that is 'Life'.