Where can I find any actual pain point or problem to solve?

I have been trying hard to find a great pain point to solve and it is really hard to find an idea. I have already built a useless product, but now I want to find a big problem, do some research get to know the customers, communicate with them and solve the problem. But I do not know where to start, what pain point should I solve. I don’t seem to have any problems to be solved. So where can I find some inspiration or problem to solve?