how to unfreeze mac desktop computer
imac desktop keeps freezing . how do i reboot imac
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Easy, I can at least get you started. You need to reset smc/pmu. You do this by shutting it down with the power button, then pull out the power cord, hold down the power button for 30 sec, plug the power cord back in and press the power button. You may want to hold down Apple, Option, P and R together for 3 chimes as it's starting up. then let go of the keys and let it continue starting up. You might want to see if you can start up in Safe Mode to troubleshoot any problems. This loads only the most basic of stuff. How to do that can be found on Apple's support page for iMacs (*desktop computers) or google/yahoo.
as to why it keeps freezing.....that I don't know....
you might want to run Etrecheck, which I've heard can be helpful
johnb