After changing MS Config and rebooting.
 PC could not find boot hard drive

I was trying to install the 21H2 update on this PC.  No avail, tried all kinds of tricks.  One site said to change MSConfig to not load any drivers.  Possible one of them was stopping the install.  I could not get Windows Update to work at all.  Change MSConfig back to the setting before and I rebooted.  The PC could not find the HD anymore.  Tried Win10 boot repair disk.  Even tried the Mini Tools program.  The files were there.  Finally found SoftwareKeep dot com website.  They said to boot with repair disk, go into CMD and type in these commands (not that dot)  Took all of 30 sec after 2+ hours of attempts to boot.  You will see a "command complete" after a few seconds.

·         bootrec /fixmbr   (there is a space after each bootrec)

·         bootrec /fixboot

·         bootrec /scanos

·         bootrec /rebuildbcd

Exiting the "command prompt" The program said reboot to "Windows 10".  Before it would always say Win7 which it was upgraded from.  I had a Win10 repair disk.
I rebooted and everything is back to normal.  It did state "Windows had to fix some thing, please reboot" on the first try.   I got back into the BIOS and put AHCI back on after that warning.