mac not booting

Hello! I was working on my laptop and suddenly a kernel panic (that's how it's called on forums) happened (with those chinese characters that demand an instant restart) and then my mac restarted. Then it took too long (around 10 min) for booting (showing apple icon and the loading bar properly)...

I have a Mac Pro 3,1 from the range of 2009-2012, Xeon e5 542 it originally came with a GTX 680 but i replaced it with a GT 740 and worked just fine, i also replaced the hard drive with the OS because it was faulty, the computer seems to have no bios whatsoever, i had an hdd with windows 10...

Hi there, I have acquired some iMacs from 2009 which have had windows 7 put on them for whatever reason. I'm trying to get macOS back on them but whenever I boot them up (current OS is corrupted btw) I get a blank grey screen followed by the PC style 'No boot device available press enter to...

Eh, I have to calm down after these odd issues. This was a new one for me though. Kind of started overnight, I put my older iMac to sleep, but it restarted by itself about 90 min later (it's done this before, random times). I'll get up, wait until the desktop appears, icons load, then shut it...