Suddenly gone incredibly slow

MisterEd said:

Before you restore anything from anywhere you need to run antivirus scans on all internal and external drives to make sure there aren't viruses there. Even if you reinstalled Windows and restore anything from the Windows.old folder you risk bringing back any viruses until you know whats there has been scanned for viruses first.

Errors on drives mean anything on them including backups could be suspect. You to scan all drives (internal and external) for errors. To test a drive:
Open a command prompt with administrative privileges and type for the C: partition:
chkdsk /f C:

You can do the same for the other drive letters.

All clear! The cause was a flaw in MS recovery software.

meditek said:

All clear! The cause was a flaw in MS recovery software.

What MS recovery software are you talking about?

MisterEd said:

What MS recovery software are you talking about?

The code that enabled MS to overwrite my Win installation and scramble all my data in the process,

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Megahertz said:

Did you tested the drive for issues with check disk?
If you can boot from the drive that works normally, open a CMD window as administrator and type:
chkdsk x: /f (replace x with the drive appropriate drive letter)
It will say your disk is in use and ask if you want to un mount it = yes

C: had a few errors but other disks were fine. Haven't noticed anything different since running it though. Virus checks all negative.

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Megahertz said:

Try a Repair Install Windows 10 with an In-place Upgrade

Forgot to say the repair got my speed back. I am now on top of the disassociations and Mozbackup restore worked onFirefox and Tbird. I am now a happy bunny. Someone suggested I check for viruses with ChkDsk!

Apart from my settings loads of stuff like pictures, programs and music just vanished.I would advice hanging on to old.windows till you're sure you've extracted everything you can.Been at it for 4 days and still finding bare areas.
Thank you all for your input. BTW the reason my Acronis backups didn't work was because Acronis 2019 has a bug that changes backup type from FULL to INCREMENTAL behind your back and I had deleted a few of the chain in ignorance.