Enterprise gurus love this question! They ask you, "before you embark on a quest to change the world, tell me what's wrong with the way things are. If it ain't broke, don't try to fix it."
I call bullshit. Whether or not something is a problem depends on who you are, what your understanding is, and what your values are. It also depends on how you define problem.
A problem is a lack, or an obstruction. It's something that prevents your customers from getting to where they want to be. To sell your solution, you need to first convince people that they really want to be where you want them to be. Then they have to agree with you that there is a problem, something stopping them. Only then you can try to sell them your solution.
So what problem did JK Rowling solve when she wrote Harry Potter? Do you think 12-yr olds were sitting around complaining about the lack of reading material, or that publishers were eagerly waiting for someone to walk in with a product that kids really wanted? If so, why did all the experts refuse to publish the book?
How about Copernicus, trying to justify staring at the skies all night? Did he ever say "people don't know the Earth is not at the centre of the universe, and this is a problem," or did he just do it because he thought it was a cool thing to do.
When Goddard started building rockets to go into space, he had no idea what the applications were for his technology, beyond exploration of a new frontier. Most people thought he was wasting resources, because he wasn't solving a worthwhile problem. But that was before anyone built on his inventions for GPS, communications, weather forecasting, environmental monitoring, looking at your house on Google Earth, or asteroid mining. They were all in the future when he started, unforseen, just like nobody knew about online porn when they invented the internet.
Every great success, every world-shattering discovery, is the result of someone deciding they wanted to do something for it's own sake, not because it was solving a problem. The problem-solving, the applications for the innovation, they all come later. But when we start on our quests, we usually don't know where they're leading us.
Nobody knows what new technology is going to be used for, only that whatever problem we think we're solving, it's not usually the one people want us to solve. So there's not really any point asking an entrepreneur what problem they're trying to solve. Instead, ask them what cool thing they're doing and try to think of a use for it.