I am using ArcMap Desktop 10.2.1. Python window was working fine then one day I opened the python window and got the following text in the window:
"F1 show help for current cursor location.
F2 check the syntax of the current line (or code block if in multiple line mode).
ESC cancels the current operation.
Shift or Control Return will enter multiple line mode. To exit multiple line mode (execute the code block) enter Return on the last line.
Access the history of commands using the up and down arrows on the last line.
Right click in the command pane for additional options."
No prompt. I don't seem to be able to enter any commands.
Have you tried Resetting your ArcGIS application profile
Also, are you getting the same problem if you open a new mxd? if so, some of these steps may help https://community.esri.com/docs/DOC-7545 even if you are not actually crashing.
If none of those, find out if there were any updates on your machine, including a software that maybe installed a different version of python and/or changed the path.