How can I normally start my iMac after a botched update to macOS High Sierra?

[aleaf]

I tried to update my 27-inch iMac (currently with Sierra) to macOS High Sierra which has totally messed it up. (I believe my iMac is a 2010 model, as I remember purchasing it new in box in 2011, but it was advertised as the older model and purchased on a discount). My wish to update started with a problem in my wired Apple keyboard; keys like caps lock, tab, escape stopped working for the last few weeks. I tried fixing it by trying different things in Settings (based on recommendations from various sites); nothing worked, so I hoped updating the OS to a newer version might help. Bad idea. My iMac was thrown into a loop of the error: something like "an error occurred while verifying firmware" or something. From there, it's all got really complicated. As I was trying different things to start my computer normally again (at this point, I didn't care about the keyboard keys or updating to High Sierra; I just wanted my computer back), I might have even mistakenly erased the HD or something. I realized this when I wasn't seeing any disk to choose to restore the system from my time machine or anything. All I saw was my external hard drive/backup machine (G drive).

Please don't recommend starting the iMac by pressing Command+R keys or such, because I suspect my keyboard has stopped working entirely since none of those suggestions worked. Moreover, before trying to update to High Sierra, one of my attempts to make my keyboard keys work was to set the command and control keys as capslock and escape keys (since those last two keys had stopped working, as noted before, and I needed the capslock etc keys more than command/option; or so I thought, argh). So, now my keyboard cannot help me boot my computer in the safe mode or anything. How can I normally turn on and use my computer again? This is terrible with impending project deadlines. I'd greatly appreciate any help.

P.S. My iMac has also been terribly slow for a long time now. I wonder if it's burned down completely or something. And the update attempt was the last straw. I have to admit I didn't have time to figure out what is causing it. Whether is a virus or maybe even virus protection software (these problems might have heightened after installing avast software, for example--I am not sure).

[DaveLembke]

Is yours on the support list under system requirements at the link below:

https://en.wikipedia.org/wiki/MacOS_High_Sierra

Did you get this OS update through normal means through Apple, or are you attempting to install it some other way?

Do you have your original installation media to set it back to new factory install?

Is there a computer repair shop in your area that can help you diagnose problems with the Apple hardware that you might not be able to test yourself?

[aleaf]

Yes, that is the system I tried to upgrade to (my current os is sierra).

Yes, I clicked on update through Apple.

I think I do have some CDs for the original settings-I can check. But I was kind of hoping just being able to get rid of the high sierra error and log into my imac as usual. I believe factory settings will erase everything. While I do believe my external disk should have backed up my stuff, I cannot be sure. I guess I can test to see in a different computer (Borrowed laptop).

There might be a shop around but was considering it as a last resort (esp. for a larger computer and when I don’t have much time outside of my work currently) and see if there’s a way to fix this on my own first.

[DaveLembke]

Looks to be a common issue with failed updates making a keyboard malfunction: https://apple.stackexchange.com/questions/254140/my-usb-apple-keyboard-stopped-working-after-upgrading-to-sierra

[aleaf]

Ah! Thanks for the link. Frustrating issues