In these cases there’s very little that you can do once the problem occurs except force a restart (hold down the power key for a few seconds). System crashes/freezes, when the whole system has become slow or totally unresponsive and you can’t even use the mouse or keyboard.In these cases it’s usually possible to force the application to quit (hold down CMD + OPTION + ESC and choose the application) if it hasn’t already done so, and then continue to use your Mac normally Application crashes/freezes, which are typified by the appearance of the multi-coloured spinning icon affectionately known as the Spinning Beach Ball Of Death (SBBOD), or an application-specific error message saying it has unexpectedly quit.Applications competing for simultaneous disk access and other resources.Too many applications open at once using up a lot of memory.Resource-intensive applications that heavily use the CPU.Not enough system memory for applications to run.Some of the main reasons that Mac’s may freeze or crash are: