arcgis 10.3 - Troubleshooting import arcpy gives ImportError: No module named numpy?

While I try to load the arcpy module in arcGIS 10.3.1 I get the following error message:

    Runtime error 
Traceback (most recent call last):
  File "", line 1, in 
  File "c:\program files (x86)\arcgis\desktop10.3\arcpy\arcpy\__init__.py", line 24, in 

    from arcpy.toolbox import *
  File "c:\program files (x86)\arcgis\desktop10.3\arcpy\arcpy\toolbox.py", line 359, in 
    from .management import Graph, GraphTemplate
  File "c:\program files (x86)\arcgis\desktop10.3\arcpy\arcpy\management.py", line 26, in 
    import _management
  File "c:\program files (x86)\arcgis\desktop10.3\arcpy\arcpy\_management.py", line 14, in 
    import _graph
  File "c:\program files (x86)\arcgis\desktop10.3\arcpy\arcpy\_graph.py", line 27, in 
    import numpy
ImportError: No module named numpy

How to fix this?