The update icon had a red x in it. When I opened it, it said it could not refresh.
I tried to refresh and rcd box with message saying it could not update. I cannot copy that message now due to update manager is grayed out.... On Linux.org forum I had found a fix which I tried. THe questioner posted the message which is I think same message as I got :
"Could not download all repository indexes.
The repository may no longer be available or could not be contacted because of network problems. If available an older version of the failed index will be used. Otherwise the repository will be ignored. Check your network connection and ensure the repository address in the preferences is correct."
The fix had me edit the base and code mirrors by choosing the fastest one.
The instruction said : "It will throw open a message at the bottom of that window telling you 'Ypour Configuration has Changed...click OK to update your APT cache."
I did not get that message but went ahead and updated cache.
I saw an option to "enable source code repositories", but did not do that.
Now the update icon is just white, no more red x, and update manager is "finding the list of updates" and is all grayed out, not usable.

I am a total newbie. I did have a way from a friend to update in terminal.
When I do that, what stands out to me is
W: http://www.openprinting.org/download...2/Release.gpg: Signature by key F8897B6F00075648E248B7EC24CBF5474CFD1E2F uses weak digest algorithm (SHA1)
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://repo.skype.com/deb stable InRelease: The following signatures were invalid: KEYEXPIRED 1624268195 KEYEXPIRED 1624268195 KEYEXPIRED 1624268195

Prior to this, I had made a change trying to connect my printer to this laptop.... Could that have caused this update problem?
I could post the entire terminal update results if that would help...
What do I need to do to fix this update problem ?

Nope.

Mint 18.1 went End of Life back in April 2021. The Mint repositories are no longer available which is why you could not update your system.

The problem with upgrading to a newer version is that you need to update 18.1 to 18.3 before you can upgrade to 19 which are also not available anymore.

It looks like you changed the repositories to something different but you did not post that information.

The "best" way to fix the update problem for a total newbie is install the latest from scratch...

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michaelk,

Can a new install be done while my old version remains on my computer ?
Or will it need a backup done b4 it is installed ? ?
Which new version do you suggest ?

The latest is 20.2. I think my Mint virtual machine is 20.1 at the moment.

It is possible to dual boot assuming you have the disk space but you would need to create some unallocated space which depends on how the drive is currently partitioned. Be sure to use the Something else option or you will overwrite 18.

I don't know if Timeshift is available on 18.1 but that would be one way to create a backup assuming you have available space and a good idea.

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ALWAYS ALWAYS ALWAYS have your data backed up to an external drive!

Cause if you HDD dies, without having your data on an external drive, you'll either lose it or have a big, complicated job recovering your data.

And do a backup before doing any install.

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Thanks much michaelk !