Q: Automatic correction of plurals

That would mean doing it in a host of applications. What is more important, I have not used and never want to use 'Correct spelling automatically'; I find it a great time-waster, especially when typing technical terms or foreign words, (whereas 'Check spelling while typing' is very helpful).

I have temporarily gone to System Preferences > Language & Text > Text and, under Substitutions entered various things like GPs and PCs both in 'Replace' and 'With'. In an attempt to find a more comprehensive solution, I chatted online with Apple technicians, and was advised to go to (my name)/library/preferences and delete com.apple.systempreferences.plist and then restart the computer.

This did not work. I shall eventually have to face using a new profile/user account and transferring everything from my old one to the new one unless some inspired reader of these discussions comes up with another solution. Are there, for instance, other preference files, .plist or otherwise, that I could try deleting?

Thanks for further suggestions. But if I did that, would I not have to reset preferences in every application in my applications folder? And what Login (Ligin?) items do you mean? Where?

Well, I tried moving the entire prefs. folder to the desktop. This did not cure the problem, so that demonstrates (as you have said) that it is not a preferences problem. I then found that I could not replace the prefs. folder, so I replaced its contents — and found that nevertheless some things had changed, so I have spent some time getting them right again.

There are no untoward log in items in my list as far as I can see. Antivirus? Only ClamXav, which I have had for ages.

I back up my system periodically, both with Time Machine and with CCC.  Apple advised me to create a new profile/user account and move all my files and settings across to it. But the Apple document 'Use Time Machine to back up or restore your Mac' does not give instructions for migrating from one profile to another within the same machine. Do you, or anyone, know of a document that does include this? For Mountain Lion? Thank you again in anticipation.

The problem is solved! You were quite right: it was a log-in item! It was Typinator — I think it only arose with a recent update to v.6.9, but I may be wrong about that. I have now written to the developer, Ergonis, and am awaiting a reply. Thank you for your patience in replying to my posts.

But now a new disaster has overtaken my computer. The sidebar with my favourites has gone, I cannot even access my home folder or my Library, I cannot find anything in Finder preferences that would help. GO > Go to folder>Library or > (my name) does not help, either. All these just return 'Folder cannot be found' (which might have something to do with Spotlight restrictions).

As a minor consequence of all my previous efforts, the menu bar at the top of the screen has now got an elaborate, patterned background that makes items hard to decipher. But I can live with that. I cannot live with being unable to access any of my folders — documents, information, applications, etc.

Oh, I didn't see this when I wrote my cri de coeur below. No, it did not occur to me that Typinator was a text helper, I am afraid.

Further to the above, in my preferences folder there is a huge host of Finder preferences (see attached screen shot). Should I delete them all?

I have got my sidebar back — but only by restoring my whole HD from my last Time Machine backup, and then deleting Typinator from the log-in items again. The menu bar still has that irritating coloration, though.