Python error - IDLE's subprocess didn't make connection. Either IDLE can't start or personal firewall software is blocking connection
Delete all newely created .py files in the directory with Python. for example random.py, end.py - that was my problem that caused the same notification window. Reason in filename conflicts.
It may be a common problem that happens when you have in you current directory a file with same name on one from Python (references : Can't run Python via IDLE from Explorer [2013] - IDLE's subprocess didn't make connection)
It seems it can also happen if you have incorrect environment variables such as HOMEPATH USERPROFILE (references : Issue 14576: IDLE: inconsistent use of HOMEDRIVE, HOMEPATH, and USERPROFILE on Windows)
I've found another related question : Python IDLE subprocess error?
My advice if the answer is not there : google may be your friend ! The 3 clues above come from there :-)
The fix is here .
Open task manager, kill pythonw.exe, if you find 2 instances or more. Should work after that.