Apple Mac: When your computer keeps switching itself off
Over the past couple of weeks I have been surprised on several occasions to find my iMac (Retina 5K, 27-inch, Late 2014) switched off. I normally leave it running, with power-saving enabled, so all I have to do is wake it. I didn't pay much attention at first, suspecting the possibility a brief power outage. But then it began to happen more frequently.
Yesterday, after my return from Biévres, the iMac began to switch off frequently, too frequently for coincidence. Every time it restarted automatically but froze as the various start-up programs were loading. Eventually it was locking up almost immediately after starting up. As a Mac user for some 11 years, I had never experienced this behaviour before. I was fully prepared for a visit to the Genius Bar and, before you ask, I do have up-to-date backups so it would be no hardship if Apple wanted to trash the disk.
As a final resort, though, I decided to reset the PRAM or Parameter Random Access Memory. This controls a whole host of core stuff that you wouldn't normally want to mess with. But resetting the PRAM is often a way of overcoming unusual manifestations such as the one I've been experienced. The good news is that it worked.
Before doing this—after all it isn't something you do every day and I needed a refresher course—I checked the procedure. This article at trendblog covers all bases, including battery-powered MacBooks and Pros. With battery-powered Macs there are extra steps, but for mains-powered iMacs, Mac Pros and minis the procedure is simple:
- Shut down your Mac
- Press the power button and then immediately →
- Press and hold Option-Command-P-R
- Hold until you hear the startup sound twice
- Release the buttons and let your Mac turn on normally
The bit about listening for the startup gong to sound twice is interesting. Other guides I've seen mention waiting for it to sound only once. I recollect that last time I reset the PRAM I waited only for one startup sound. Still, I held down the keys for a good minute after the gong sounded for the first time and, just when I was about to give up, it sounded again and the computer shut down. When I restarted the machine, all was working without any initial problems. It's business as normal and I'm glad I've been spared the unwelcome prospect of lugging the very heavy iMac to the nearest Genius Bar.
If ever you get unusual happens with a Mac it is worth giving the reset PRAM routine a spin before taking more drastic action. According to the experts at trendblog this simple action can solve many annoying problems.
Note: Before resetting the PRAM or carrying out other investigations I recommend unmounting all external disks and USB connections other than the mouse and keyboard cables (if present).