OS X Yosemite: If a keyboard shortcut doesn’t work
It’s possible to have keyboard shortcuts for one app that conflict with another app. For example, Command-Space bar opens the Spotlight menu, but in another app it might be used for switching between different input methods.
Choose Apple menu > System Preferences, then click Keyboard.
Click Shortcuts. A yellow warning triangle appears next to conflicting keyboard shortcuts. Click the shortcut, then change it.