I just tried to install the 64-bit "full installer" version, for
all users with the default options. This is on a PC that hasn't had
3.5 installed before, and doesn't have Visual Studio 2015 installed.
When it got to the step "precompiling standard library" I got an error window pop up saying "python.exe - system error. The program can't start because api-ms-win-crt-runtime-l1-1-0.dll is missing from your computer. Try reinstalling the program to fix this problem." All there was was an "OK" button. Pressing that told me "Setup was successful" but then "py -3.5 -V" gives me nothing (no error, no version, just returns me to the command prompt). Same result if I do "& 'C:\Program Files\Python 3.5\python.exe' -V".

Python 3.5.0a2 (64-bit) is showing in my "Add/Remove Programs".

This is Windows 7, 64-bit.