When this happens (the window is too small and won't resize) it's most likely a Preferences problem.
I first suggested a Preferences reset by keyboard: Windows - Hold down CTRL-SHIFT-ALT immediately after you double-click the PS icon and answer "Yes" to delete the settings file.
If that does not work, do this:
Go to C:\Users\[User NAME]\AppData\Roaming\Adobe\Adobe Photoshop CC 2014
and rename Adobe Photoshop CC 2014 Settings folder to old.Adobe Photoshop CC 2014 Settings
Restart and Photoshop should rebuild the settings folder.