imac late 2012 27inch keeps shutting down
My iMac, seemingly when it ought to be going to sleep, and occasionally while I'm working will just turn itself off. Buttons fail to restart it, and the only temporary solution is to remove the power cable, wait a few seconds and press power once more. Very annoying. Any ideas please? thank you.
iMac, OS X Yosemite (10.10.3)