While Macs are very stable, they can start to have problems if you load too many programs or load an unstable program. The most common symptom of a crashing Mac is the spinning pinwheel of death (SPOD). This is a multicolored pinwheel cursor that appears when your Mac is attempting to do something and is having trouble. Here's how to unfreeze your frozen Mac.
1. Quit as many applications as you can. When your Mac freezes it's often because of one specific application, but if you don't know which one is causing the problem, it's best to quit them all.
2. Force quit the apps that you can't quit through regular means. To get the Force Quit menu, you can hold down Command + Option + Esc or follow one of several other options.
3. Restart your Mac. This will clear up most problems.
4. Hold down the power button for 10 seconds if you can't restart your Mac via software. This will force your Mac to shut down. If holding the power button down doesn't work, pull the plug so that your Mac is not getting any power. Leave it unplugged for at least 10 seconds.