Botched High Sierra installation

[mpavilion]

Just tried updating my 2013 iMac to High Sierra, and got the following error msg. at the end of the process: “com.apple.DiskManagement error -69854”.

Now when I try to start up, the status bar fills about halfway; then I get a multi-language msg. saying, “Your computer restarted because of a problem. Press a key or wait a few seconds to continue starting up”. If I wait, it keeps trying (and giving me that same msg.), but won’t boot all the way up... eventually, I just get a “NO” (circle w/diagonal cross) symbol.

This seems bad. What do I do? We have an external drive w/Time Machine, so I’m not totally freaking out (though I stupidly didn’t back up immediately prior to running the update).

 

[nambuccaheadsau]

Does the iMac have an SSD installed? Where did you get the Installer? Did you make a flash drive stick with HS on it?

Suggest you get HS from the App Store, use DiskmakerX to burn it to a flash drive, boot from the stick, erase and format the hard drive, and do a nice clean install. Then hook up the TM drive and use Migratation Assistant to bring things over.

 

[mikehalloran]

Does the iMac have an SSD installed? Where did you get the Installer? Did you make a flash drive stick with HS on it?

Suggest you get HS from the App Store, use DiskmakerX to burn it to a flash drive, boot from the stick, erase and format the hard drive, and do a nice clean install. Then hook up the TM drive and use Migratation Assistant to bring things over.

All good suggestions but reset the NV Ram first.