[GreenNight]

Could be useful IN a startup, but not AS a startup.

AFAIK YCombinator is for creating startups, not for letting outside people be a part of one.

You want to prove your will? Ask your neighbours, parents, friends, people you find in the street, ask them for what troubles them, what little things they have to do what would rather not. Find a way to solve it, charging money, low enough that they would rather pay, high enough that you cover costs.

Then you either have a nice startup of your own or at least you have some experience that you can share here. Repeat until success or bust.