Unity suddenly stopped working when I pressed play

My error: Invalid editor window UnityEditor.GameView UnityEditor.EditorApplication:Internal_PlaymodeStateChanged()

3 week old comment in response to another person and not me on a Unity forum:

One thing to try is deleting the Unity preferences file. On a Windows, you can find the prefs in C:\Users\USERNAME\AppData\Roaming\Unity\Editor\Pre ferences

After editing a script Unity stopped working on me when I tried to play my game and any of my other games and gave me the above error. Keep in mind it didn't give me a message saying Fix Compiler errors: the three buttons at the top turned blue and the play and pause buttons highlighted as clicked on as well. I tried reinstalling it. I can't find the file the person who quoted the above refers to. It doesn't exist anywhere in my computer and I tried searching for it in multiple ways. Could someone tell me exactly where this file is? In the Unity Folder under the Editor subfolder right? So what in the editor am I looking for? Like I said my computer says this Preference file doesn't exist. Is it because I have the recent 3.1.0something f.4 version instead of the version b4 that? Do I have to delete something specific in my project folders or import something instead? If deleting that file won't work for some reason(ex. if it really doesn't exist for me) what will help? Any help would be really appreciated! Thanks in advance!!!

Side Note: What tends to cause this? All I did was edit a script and try to play the game and then this error came up all of a sudden.