I recently had to test connectivity with another computer on my home network. As I had always done, I launched CMD.EXE and a black, familiar window is opened, with a title saying that I am the Administrator (wow!). I type PING followed by the URL, and it says that PING is not a recognized command. I make a quick search for PING.EXE, and it is in Windows/System32. I then repeat the command using the full path, and it works. It happens that System32 is not in the PATH of the shell.
How did it get removed from the path, and how should I put it back?