2009 mac mini: gray blank screen; boot commands not working
This old mac mini (Intel Core 2 Duo model, pretty sure it has 8GB RAM) has been good to me, but is super slow now and the disc drive hasn't worked for years. I thought I'd try and convert it over to a basic linux box and get another couple of good years out of it. I tried to setup a linux bootable USB drive (using balena, after first formatting drive as instructed - guid partition, etc.).
After trying to boot to the drive and use mac boot commands (like Opt, Cmd-R, or Shift), it would immediately boot to grey screen (with no other icons/visuals). Booting without boot commands, I went back into MacOS and went into SysPrefs > Startup to see if it would detect the USB drive from there, but it didn't appear.
I went over to a WinPC and created a linux boot drive from it and tried to use the USB drive in mac mini after that, but it still wouldn't work. Unfortunately, at some point around the same time (it wasn't immediately after trying to boot to USB), I can no longer get past the grey screen (with or without mac boot commands and without any peripherals except a USB connected keyboard). I'm not sure where to go from here...the ONLY thing that appears to work is if I do PRAM reset mac boot command, it will reboot after I hold it for a few seconds (less than 10s) and will keep doing it...no other commands seem to work.
I kind of doubt this would be a hardware issue given that the computer was working fine before I started messing around with diskutil...but, if that's where I'm at then I guess maybe it's time to recycle this. But, not willing to concede quite yet!
Any ideas how I can get to either a bootable state or at least a state where the mac boot commands will work (so I can get to disk utility, mac recovery, or safe mode - anything really)?
Mac mini, OS X 10.11