Ask Max: iMac Not Waking Up
I normally leave my iMac on 24/7; but it does go to sleep during most of each 24 hour period. Recently, I have noticed that the iMac will not wake up from sleep in the mornings when I want to check for emails. In fact, it appears dead. I cannot hold down the button at the rear to get it started. I must first pull the plug and wait for a few seconds before plugging the power cord back in. Then I can press the power button at the rear and it comes up. However, a meaasge appears saying that the Mac was not properly shut down. The iMac does not feel hot, only slightly warm along the top. It appears that I have a power supply problem. What do you suggest?
While it may indeed be an issue with the power supply unit within the iMac, it may also be that your PRAM/PMU battery has stopped holding a charge. This can cause issues like failing to wake from sleep, forgetting what the time/date is if the unit's unplugged, and even failures to start up normally.
It's certainly worth trying to reset the PRAM and the SMC first, but I don't have a lot of confidence this will work at this stage.
It would be a low-cost option to test prior to having a power supply replaced. Should a battery not resolve the issue, then the only other real option would be to check it into an authorized service center to have the unit bench-tested.
Moving forward, I suggest you at least restart your Mac once a week and let it rest overnight at least once a month. Servers are made to run 24/7, but computers really should have a rest now and again.