No entry sign
I ran first aid as suggested by another post, tried to re install OS and get the message, 'The recovery server could not be contacted."
iMac 27" 5K, macOS 10.14
Question marked as
On another Mac, download the High Sierra Installer —that installer should be just shy of 5 GB in size, if you've gotten the correct one—and then build a bootable installer, transfer that bootable installer to the problematic Mac, and boot that.
One of the triggers for folks to be going through this whole Recovery and re-installation sequence can be a failing hard disk drive—that obviously on a Mac with a hard disk drive. That hard disk drive failure tends to show up as slowdowns, beachballs, corruptions, and app and system crashes.
If the hard disk is failing in this case and if you're interested in keeping this Mac for a while more, replacing the hard disk drive with an SSD can be a reasonable upgrade. OWC is one of the vendors with a reasonable reputation for documentation and support, if you might be considering performing the swap yourself. The difficulty of a hard disk drive swap depends on exactly which Mac is involved.