I have an old (2011) Mac Mini, which was running High Sierra. It was running perfectly well, but really slowly, for reasons I couldn’t track down, so I thought I’d try resetting the PRAM. I shut it down and restarting, holding command-option-P-R. It chimed a couple of times.
Now, it won’t start. When I power it on, it chimes and the white LED illuminates, but that’s it. There’s no video output, so the HDMI-connected screen stays blank.
I’ve tried unplugging it for a while and resetting the PRAM again. No dice. I’ve opened it up and re-seated the RAM, just in case, but it’s made no difference. The only devices connected to it are the keyboard and a wired mouse.
Yes to all. The power is fine: the machine chimes and the LED illuminates, as I wrote. It was working, but slow; I restarted, resetting the PRAM; and now it won’t start. I didn’t touch the monitor, the Mini or any of the cables. All I did was hold down those keys.
I’m sure it’s software/firmware. I just can’t think how to proceed now.
Does the machine show up on your local network, can it be reached by screen sharing or file sharing? If so, it has probably lost its monitor resolution settings.
Do you have a known good bootable backup for this machine (doesn’t need to be High Sierra, as long as the machine can run it. The original install cd would do. A TM disk also.) Attach the bootable drive, reboot the machine holding the option key. This gives you the Mac Startup Manager, which gives a list of bootable systems to choose from. Choose the system you like to boot. If this will not work its either the monitor or there is some sort of hardware problem.
If you are still stuck, I’d definitely temporarily change the cables.
Just last weekend, I was baffled troubleshooting an iMac (running High Sierra, coincidentally) that wouldn’t boot. Finally on a lark, removed an Apple Lightning to USB cable that was connected to an Apple wireless keyboard, and boom, the iMac immediately booted successfully.
I couldn’t even see any fraying in the Apple Lightning-USB cable, but the evidence was overwhelming (or else abnormally coincidental).
Have tried reseting the SMC? For the mini it should be:
Desktop computers
Shut down your Mac, then unplug the power cord.
Wait 15 seconds, then plug the power cord back in.
Wait 5 seconds, then press the power button to turn on your Mac.
After fiddling a bit more, I gave up and went to bed. Bizarrely, this morning it has completed startup, although it’s even more agonisingly slow than it was before. I suspect the disk is dying. I’ll clone it to an external SSD and see what happens when I try to start up from that.
If that works, replacing a hard drive (either with another hard drive or a SATA-based SSD) isn’t too hard to do. There are a lot of steps, but none require any special training as long as you are careful to follow the instructions.
To replace the lower drive (or the only drive for a single-drive mini):
To replace the upper drive (or install a dual-drive kit to add a second drive) has a few more steps:
I used Chronosync to make a bootable backup copy of the internal HD onto a Sandisk external SSD. It took about 8 hours for about 350GB, which seemed an awfully long time.
However, on booting from the SSD the Mini now runs at normal speed. Hypothesis supported.