IDLE is the Python development environment.
You need to “kill” all the idle processes. A dangerous shortcut is
pkill python
It will give you a warning message but usually works
Or, you can say
ps -ax
Which shows you all (-a) the processes. Then, kill the process by their ids (PID)
kill <pid>
If the IDLE shell is acting weird with the prompts when they want to run something (like it's still executing another program), just hit enter a few times or control-c to cancel that and then execute the program again.
If IDLE is exiting completely when a program executes, then try opening the Python program in jEdit and then executing the program on the command-line/in a terminal. After testing in jEdit, try again in IDLE.