Please, don't get me wrong: I am certainly no expert, but I follow my grandmother's motto at all times.
"You can be stupid, but you have to know how to help yourself."
Here's one step you possibly could try. It is a German AntiVirus Solution. Alas I do not know how you could get it outside of Germany. You need to buy a certain edition of a PC-Magazine ("c't", well reputed, ~€10,-) (If you're interested I can find out for you)
The basic idea is to run the AntiVirus software from a DVD or Stick using Ubuntu while the PC's OS is not running at all.
I've translated some info from
Desinfec't from heise Security is the successor to Knoppicillin and scans your computer for viruses, Trojans and other malware.
Unlike conventional virus scanner software, Desinfec't does not run as a Windows program, but as a live system on a USB stick or DVD. This allows the software to better analyze a potentially infected Windows system because it is not running. This means that existing malware cannot actively hide from the scan and could be detected more easily.
The operating system used for Desinfec't is the Linux distribution Ubuntu. Windows users should not be put off by this, as all the necessary icons are located on the desktop of Desinfec't and perform the described function with a simple double-click.
Download and use Desinfec't
The current Desinfec't 20 22 is available in the c't special edition and on a USB stick. Buyers of the magazine will find information on how to download an ISO image for Desinfec't. Buyers of the USB stick will receive Desinfec't as well as a PDF version of the c't special issue. On heise+ you can also find a detailed manual for Desinfec't 2022
Once that has failed ...
- Create a Linux-Boot-Stick and run ClamAV from it. Under Linux of course; that's the idea: not using Windows.
- Have you ever tried reproducing your installation on a different but similar machine (same OS, same installation)
- Taking this stuff to your PC store for them to take a look at?
- Your measures don't seem particularly cost-effective. If you calculate your hour with only $20,- ...
If one of my machines was giving me that much aggro, I would skip the cause and effect research and just rip out the HDs. And start with a newly purchased, pristine HD. (Manual reinstall, no image)
On the other hand, if you want to write the definitive article on how to solve this damn problem ...
@Levers, I am so sorry, but my 2 cents are probably really only worth 2 cents