If you think you spot such a problem, use your colleagues and the library to make sure it hasn't been plucked yet. Finally, you can identify new interesting problems. If your field is interdisciplinary, ask people in the other discipline what they think is interesting. In fact, ask them why they think computer scientists are irrelevant. In many areas, the data have a way of suggesting their own problems.
Linguists can find unexplained phenomena in any magazine article.
Systems programmers can collect data on actual disk access patterns and study it for regularities to exploit. Theoreticians of programming languages can look at real programming languages, and graphics programmers can look at real photographs and movies, for effects that they don't know how to capture. There's lots of research out there, so you have a choice about what to work on. That means you can easily spend too much time on any task you start, especially if stubborn perfectionism or an inferiority complex leads you to feel that your work is never good enough, or if you're subconsciously trying to put off that scary next phase of your research. Don't spend eternity on background reading.