How to prevent HP Pavilion 23xw from dimming with Windows 10 64bit?

Is this on AC or battery?  Most notebooks dim when on battery automatically.

This is on AC.  And it's for a desktop.

Check the power settings of your OS. For example disable the option "Enable adaptive brightness".

I had that on one client machine with Windows 7. Download the newest video driver for your machine and install that. Reinstall the current driver if it is the newest.

If the computer vendor has power management software, upgrade or reinstall that.

Finally run System File Checker. Open cmd.exe with Run as Administrator and run SFC /SCANNOW twice. Close out, shut down, start up and test.

you can also test if changing the energy setting makes a difference
set it to never power off

Will try some of these suggestions

Enable adaptive brightness is already OFF
Turn display is already set to NEVER

Did you try reinstalling the video driver?  
Try a different monitor to see if that works.

I had a previous monitor and I had the same problem.

I have asked several times - Have you updated / reinstalled the video driver?

If none of this works, you may need to do a Windows 7 Repair Install with the Windows 7 DVD (select the Repair option).

I have updated the video driver, not reinstalled the video driver.
Also, kindly look at the note I have in my initial request.  This is for a machine running Windows 10, 64bit.

Sorry about the Windows 7 Note.

Try reinstalling the video driver and restart.  Also try DISM (repair tool)

Open cmd.exe with Run as Administrator.
DISM.exe /Online /Cleanup-Image /Scanhealth (takes 15 - 20 minutes).
DISM.exe /Online /Cleanup-Image /Restorehealth (takes 15 - 20 minutes).
Restart the computer and test.

Not only windows itself has adaptive brightness settings, also the graphics driver software (by intel/nvidia/AMD/...) might have these settings. Please look through their settings, too.

Still dimming, all started happening after usinf windows 10

all started happening after using windows 10   <-- And on different monitors (so you said) as well.  So that means the Video Driver is likely not Windows 10 compliant.

We cannot go through the settings for you and need your feedback if you did it thoroughly. I would expect this to be a setting inside the graphics control application. AMD has this in catalyst control center and I am pretty sure intel and nvidia will have these options, too.
I see no reason to think it's a non-compliant driver.

I have Intel Graphics and I do not see any setting to dim my monitor, and it does not dim either on its own.

That's fine, John - but what about his system?
Looking at mine (intel graphics, too), there is no adaptive brightness, but some adaptive contrast setting at least , see the screenshot. So it might be the model/driver combination that has or hasn't got it (do we know the brand of the video card yet,  100 questions? I don't see it).

There is a contrast enhancement on the Graphics Control panel, but not an Adaptive Contrast enhancement or Adaptive Brightness enhancement.

Then we cannot help you. If it were broken, it would not be like this, for sure. There's some dimming component involved. Ask the manufacturers of
1 the monitor
2 the video card

where to find it. You could also compare to a different installation, of course.

Or tell us more details of the PC (not the monitor). PC manufacturer/Model or at least what video card is being used.

I may reach out to the manufacturer.

Thanks for the update and I was happy to help.