What major challenges and problems did you face? How did you handle them?
This question allows the interviewer to delve into your experiences. If you struggle to answer this question, or have no good examples to give, it will present the impression that you have faced no real challenges and therefore have gained no real experience. Any hesitation your interviewer sees from you should be viewed as you trying to choose between the vast array of challenges you have encountered and subsequently conquered.
You should follow the structure of the question in your answer and try to give an example relevant to the job you have applied for. Firstly, you should identify the challenge, describing the problems this caused. Follow it up with the thinking process you went to before arriving at the solution.
: "In my previous post as maintenance manager back-up gas turbines at a power station. We simultaneously lost 50% of our gas turbines whilst they were on load supplying the national grid. This meant we would be below the required capacity to meet demand for a peak time that was only 3 hours away. I had to immediately organise my team to investigate and identify the defect whilst ensuring the other turbines did not suffer the same symptoms. Therefore, I split my workforce leaving 3 men to watch-keep on the remaining machinery and the rest were tasked to find the symptoms. The problem was found to be a combination of a blocked filter and a seized valve. The valve was changed and the filter cleaned, which brought the off-line plants back into service one hour before the peak time. Thus averting power losses throughout the grid. Due to this incident I instigated stricter time tables on checking filters and created a maintenance routine to test all valves periodically."
This is a comprehensive answer which demonstrates the ability to act under pressure and shows what was learned from the problem. Obviously this answer would be fairly irrelevant to a job in the retail sector and therefore, your answer should reflect the job you are being interviewed for.