Couple of resets you can try, 1 at a time...
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How to reset the SMC on Mac desktop computers
Follow these steps for iMac, Mac mini, Mac Pro, and Xserve.
Shut down your Mac.
Unplug the power cord.
Wait 15 seconds.
Plug the power cord back in.
Wait five seconds, then press the power button to turn on your Mac.
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How to reset NVRAM
Shut down your Mac, then turn it on and immediately hold down these four keys together: Option, Command, P, and R. Keep holding the keys for about 20 seconds, during which your Mac might appear to restart. (If you have a Mac that plays a startup sound when you turn it on, you can release the keys after the second startup sound.)
Option + Command + P + R
If you've already tried these resets then just ignore me...
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How to reset the SMC on Mac desktop computers
Follow these steps for iMac, Mac mini, Mac Pro, and Xserve.
Shut down your Mac.
Unplug the power cord.
Wait 15 seconds.
Plug the power cord back in.
Wait five seconds, then press the power button to turn on your Mac.
---------------------
How to reset NVRAM
Shut down your Mac, then turn it on and immediately hold down these four keys together: Option, Command, P, and R. Keep holding the keys for about 20 seconds, during which your Mac might appear to restart. (If you have a Mac that plays a startup sound when you turn it on, you can release the keys after the second startup sound.)
Option + Command + P + R
If you've already tried these resets then just ignore me...