Late 2013 27" iMac. Mojave failed with a "cannot continue with installation" message. Couldn't get computer to reboot at all. I can't try recovery mode till after 11pm UK time as I have satellite internet and the download will use a week's worth of daytime data. Rather stupidly, I decided to try option-cmd-P-R to reset all RAM. Now the Mac just continually gets as far as Apple logo and chime then reboots, Apple logo and chime, reboot, Apple logo and chime, reboot etc. Any ideas much appreciated.