The question

Hello,

In the past 2 year I?ve develop my career as Technical support consultant in a independent contact center solutions company.

When the customer call?s for help the sentence is pretty much the same:
?This was working and Know is not. I didn?t change a thing. It just stops?

This is not real. 99% of the cases after solving the problem the customer confessed he change this or that but he didn?t knew this was relate to the problem.

Due to this my major goal in the past months is to find ?the question?.
Did you change something doesn?t work. I?m trying to find a perfect question to use instead. Something that will lead the customer to tell me exactly what did he changed.

Ideas?