While restoring service to a user is an important factor in solving a problem, the other three answers are the most important and most valid objectives, especially in a long-term situation.
Problem Management also needs to consider how problems and their resulting incidents can be prevented in the future, managing problems throughout their lifecycle, and how recurring problems and incidents can be eliminated.
Restoring service is likely only a temporary fix and may lead to even more problems if the underlying cause is not identified and fixed so it does not happen again in the future.