I am using PyCharm v2.7 build 125.57. I just witnessed a strange problem I have never seen before. The problem was that PyCharm's editor window would not open. Everything else worked. Tabs would even appear above the Project Window for whatever python file I had double clicked in the Project window. I could even run the file and see the expected output in the Console. But no tab appeared above where the editor window normally shows up. Also missing was the 'No Files Are Opened' message which normally appears where the editor window would be if no files are open.
There are a couple of features I never used before prior to a couple of days ago, which may or may not be a factor here. Specifically, I began using CMD+MouseWheel to zoom in and out. And I switched the appearance from Default to Darcula.
Also, the problem appeared when I started up PyCharm after shutting it down with no editor windows open which is something I rarely do.
Shutting down PyCharm and restarting it did not help. What did restore normal operation was to change the appearance from Darcula back to Default, after which PyCharm does a restart.
So far, I have not been able to recreate the problem, even though I have changed the appearance back to Darcula and closed all windows before doing a restart.