Normally, the graphs in SimaPro show a breakdown of the results, showing the contribution of the top processes or product stages. However, sometimes this breakdown is not shown, due to the fact that the top processes you are analyzing are part of a loop.
This means that the process you are analyzing is also used in some upstream processes that are used in the process that you analyze. For example, electricity is needed to produce building materials for the power plant that produces that electricity, or steel is needed to build trucks that transport steel.
For mathematical reasons, SimaPro cannot show the breakdown of the results if the top process is also used as an input somewhere else in the model. A work-around is to 'break' the loop. You can do this by making a copy of the process you want to analyze. The copy will open in edit mode, and even though the underlying model is the same, the copy is not part of the looped system anymore. From this window you can use the analyze function and see the results including breakdown.
You do not need to save the copy, unless you want to use it in a calculation setup. If that is the case, make sure you give the copy a clear and distinct name, and remember that any changes in the original process must also be made in the copy.