An hypothesis is the proposed explanation that is made on the basis of limited evidence and it serves as the starting point for further investigation while a problem statement is a clear, concise description of the problems which needs to be addressed.
Problem statement is used to concentrate the focus of the researcher at the beginning, to keep him on track during the operation and at the end it is used to evaluate if the process delivered an outcome that solve the problems.
Hypothesis is used to define the relationship between two variables at the end of the research the scientist has to decide when its starting hypothesis is valid or not.