How to find what’s wrong, if anything, with my machine?

For many years, I have used PSPad as my default txt editor and it has worked great. However, starting a short while ago, it would regularly crash. I have no reason to believe that the issue is with PSPad, so yesterday, I ran MS Security Essentials – it found a few meaningless items and I deleted them. I also uninstalled PSPad, removed everything PSPad-related from my machine, downloaded the latest version of PSPad, installed it, and rebooted. (Also note that months ago, I removed a number of MS updates that are known to be problematic.)

The problem has not fully gone away. When I exit PSPad, I usually get a window that says “PSPad has stopped working”. What can I do to figure out the root cause of this annoying problem?

Open a CMD window as administrator and type:
chkdsk c: /f
It will say your disk is in use and ask if you want to schedule to next start = yes
Restart
Pay attention on the results, specially bad blocks, bad clusters, bad sectors etc

Back to Windows, open a CMD window as administrator and type:
sfc /scannow

If it finds any corrupted files, fixing or not, reboot and run again.

M$ is trying to kill Win 7 so you move to Win 10 and they make money out of you.
Follow the instructions on Single file with all updates - Simplix

Megahertz07: Thanks. I have done both chkdsk and scannow and nothing inappropriate was found. Also, I plan/hope to never downgrade this computer to Windows 10 (which is nothing more than spyware disguised as an operating system...)

Did you followed the instructions on the Simplix thread (disable WU and removed the telemetry)?

the newer "stopped working" comment is likely caused by the PSpad install.... its likely been updated to cover newer system requirements in W10/11..... you might actually be better off using a version that was only intended for W7

Megahertz07: Yes, Windows Update is set to not check and the telemetry updates they suggested be removed were removed (or never were installed) on this computer.