PC slow after rolling back to Windows 8.1 from Windows 10?

I think after downgrading your laptop windows have some leftovers. So, I'll suggest you to clean the 'local disk (C Drive) using the windows DISK CLEANUP tool.

No Kidding. You will once again have to download & configure the 300+ updates. Should have simply let W10 configure. I'm on W10 and love. Would NEVER consider going backwards

The main issue with W10 is the user logs on and expects miracles. Well that's not the case. W10 needs at least 1 - 2 hours to configure. No different from previous OS's which also take 3 - 4 hours post logon due to the fact there are 350+ updates to download & configure.

Once W10 has finished the installation and you are logged in and on the Desktop screen, locate the HDD light. You will notice the light to be illuminated or blinking and the Taskbar will flash periodically. Windows is now configuring the installation, meaning all Windows & accessory driver updates. Allow the system to run unimpeded until the light stops flashing (may take 1 - 2 hrs). If the unit is not equipped with a HDD light, allow the system to run unimpeded for at least two hours.

DO NOT attempt to update any drivers or run games, the configuration process is taking care of this. Do not RESTORE or REFRESH during this process. You may cause your system to CRASH.

You will run into issues if you do not allow for configuration such as programs not working correctly, slow jerky mouse movements, or sound issues to name a few.

Do not allow the computer to sleep or CPU to shut down. Change your power settings until W10 is configured

Restart & enjoy…

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P.S.

I have updated 6 laptops & 1 desktop with Home & Pro. They are all purring like a kitten