Many thanks to all those who have contributed to this topic and offered suggestions.

I have learned a lot.

 

After taking everything I could find out and cleaning then re-seating everything, the symptoms were the same so I gave up and took it to a local PC repair shop which had been highly recommended by a friend of mine.

It turned out that the internal SSD had failed and could not be recovered.

All my data was on the internal HDD so just the operating system and my program files were gone.

They installed a new 256 GB MV8 SSD and reinstalled Windows 10 using my licence key.

They even installed MS Office 2010 for me although it is probably a bogus copy.

I still have the email from MS with the product keys for Office Pro and Project so I will uninstall their copy and reinstall the licenced software.

The new SSD has a 3 year warranty which gives me a good reassurance, and the total cost was 2,500 THB so no complaints at all.

 

I also bought some USB 3.0 flash drives so I can create some bootable installation media, Macrium backups etc.

 

Much appreciated everyone. 

A bit too much, since a 500 GB NVMe drive costs 1890 baht; https://www.invadeit.co.th/product/solid-state-drives-ssd/crucial/p1-500gb-3d-nand-nvme-pcie-m-2-2280-ssd-ct500p1ssd8-p041073/

You'll note that it has a five year warranty and is PCIe Gen3 x4. Not the best of the best, but probably at least as good as whatever they fitted for you.

 

Three year warranty is poor. 

 

In addition, one would be looking at a PCIe Gen3 x4. Quite possibly you purchased PCIe Gen3 x2 seeing as you have only a three year warranty.

Examples of PCIe Gen 3 x4; https://www.jib.co.th/web/product/readProduct/30328/1471/256-GB-SSD--เอสเอสดี--PLEXTOR-M9PeGN-PCIe-NVMe-M-2-2280--PTSSDPX-256M9PEGN- 1990 baht with a five year warranty.

https://www.jib.co.th/web/product/readProduct/32923/1471/256-GB-SSD--เอสเอสดี--ADATA-XPG-SX8200-PRO-M-2-2280-NVMe--ASX8200PNP-256GT-C- 2090 baht with a five year warranty

 

Check the speeds as compared to your drive; Read Speed/ Up to : 3500 MB/s
Write Speed/ Up to : 1200 MB/s

Are they the same?

 

Whilst it's too late for you, someone else might benefit from these notes.

 

You should always clean install an OS for yourself.