1. Force quitting an app that is not responding
If an application is not responding, if it's continually bouncing in the Dock or appears to have frozen, you may need to force quit it. You can do this by holding Ctrl+Alt+[esc] to bring up the Force Quit window, or by choosing Force Quit from the Apple menu. After quitting the program, try relaunching it. If it still doesn't work it may be incompatible with your version of OS X. Thankfully, force quitting programs on Macs nowadays doesn't generally affect the stability of the system and doesn't require a restart.