IMac not booting

2013 iMac running the latest iOS will not boot. Safe mode, Recovery mode, and internet recovery do not work. Internet recovery I’ll find the computer shut down after an hour or so, other attempted boots, regular, safe mode, recovery mode will find the progress bar stall and then varies between gray screen, frozen progress bar, and occasionally the multi-language your computer encountered an error screen. Happened overnight with no previous issues. Any suggestions? Thanks.