My Windows 10 Version 20H2 will not install the update 0x80004005.

This worked for me, after the System File Check. I was surprised at how many issues were repaired.

First check the hard drive for errors.

1. Open a CMD window as an administrator.
2. Type or paste ‘chkdsk /f /r’ and hit Enter.
3. Allow the process to complete.

Then perform a system file check.

1. Open a CMD window as an administrator.
2. Type or paste ‘sfc /scannow’ and hit Enter.
3. Allow the process to complete.

I had my updates paused, so nothing was downloaded or pending install. I did not turn off any of the virus protections running, or any extra steps like that.

I then checked the hard drive for errors as mentioned above...

1. Open a CMD window as an administrator.
2. Type or paste ‘chkdsk /f /r’ and hit Enter.

This said it couldn't run right no, but would do so automatically on the next re-boot.

Before rebooting, I downloaded and ran the utility found here...

https://www.microsoft.com/en-us/software-download/windows10

The install took under an hour and had no issues. It required one reboot.

Then I un-paused Windows Update and let all the mandatory updates download including our problem 20H2. Once everything was "pending install" I rebooted when prompted and waited for the usual failure message... BUT IT WORKED! Windows Update now has the "You're up to date" message and hopefully it stays that way for awhile!

There is still one update sitting in the "Optional quality update" list...

"2021-03 Cumulative Update for Windows 10 Version 20H2 for x64-based Systems (KB5001649)"

...But I'm not going to touch it!

Hopefully this solution works for others as well.

I could not update win10 to 2H20 after trying everything suggested. I was getting error code 0x80070003 .

I dual boot Win10 and Linux Mint each on a different HDD with Linux giving me the option to boot up on the OS I choose.

To solve the problem i had to make Win10 the automatic boot OS.

I booted to Linux and used the program "G PARTED" to option Win10 as the boot OS.

I ran "Win10 Update Assistant" and it worked.

I now have the 2H20 update.

I hope this helps somebody

I’m having the same problem, but the problems I’m having is 20h2 the updates are not automatically updating and I’ve got no sound I don’t get what’s doing this because I’ve downgraded to 1909 and it automatically updates windows updates there is no problem with the sound so if I do a fresh clean install of windows 20h2 then there’s no sound on the volume icon it’s got a red circle with a white cross and you have to go into optional updates to do it manually then when you tick the box you download what’s in the list of updates then you will see the screen flicker and then I will have sound but you have to do this manually is anyone else having the same problem because I’m going out of my head here I’ve google it trying to find what could be causing this I can’t find nothing.

Been trying to update to 20H2 many times. It never work's no matter what I try.  My computer is still under warenty so I called DELL help.  I have only GOOD things to say about DELL Help.  I gave Dell control of my computer and they spent more than 9 HOURS trying to install the update.  Never could install the update.  Would go all the way thru and then say could not complete the update.  Each attempt was around three hours.   I have over 40 hours trying different things.

Rex Williams