I had similar problems after replacing a faulty hard drive.
The game changer was a thread that suggested using the System File Checker (SFC) utility on www.800error.com . "This handy in-built tool will check your file system.
- Click Start and type "cmd".
- In your search results cmd should show up with an black icon.
- Right-click it and select Run as administrator.
- If you are prompted for the admin password, enter the password and click OK.
- A new completely black window will open. You can type commands directly into this window.
- Type sfc/scannow and press Enter.
- This process will take a long time. You can minimize this black windows and work on.
Come back to the black window after a time and check if the process finished.
As soon as the SFC process finished, restart your computer. After the restart you search for Updates again."
SFC came up with a lot of fragmented files, presumably arising from the old hard disc and the files persisting. The message was that the files had all been repaired.
When I tried to update, progress sailed past where it had stopped before with error 0x80029c4a. However it did fail with error 0x80070005, a permissions error. But, when I did the last step and restarted the PC I was gratified that it sailed through the update.
If only I'd been aware of SFC when I was trying to get going again after replacing my faulty hard drive when I had to reinstall previous version of Windows 10 from an ISO file - could have saved time then too!