Python 3.5 will not install on my Windows 7 Pro machine. The observed failure is : Error 0x80240017: Failed to execute MSU package. This appears to be an open problem with Python 3.5. The same does not have any problems with the Python 3.4.1 installations.
Can you try installing http://www.microsoft.com/en-us/download/details.aspx?id=48145 and then install Python again? That installer is installing the same update for your machine as Python 3.5 requires, so our installer should skip it once it is on. Alternatively, you may get a more detailed error message.