Error: We couldn’t complete the updates, Undoing changes. Don’t turn off your computer.

This is probably because you already have a partial installation of KB2919355 which the new attempt is unable to overwrite. This results in the installation attempt being undone like you describe.

So do the following next.

Go to Programs and Features in Control Panel and click the link to "View installed updates".

In the next menu, copy/paste: KB2919355 in the Search field top right. If it's installed, it'll appear below and you can uninstall it from there.

If it's not there, close Programs and Features, right click the Start button and go to Command Prompt (Admin). Then copy/paste the following command and hit Enter:

DISM /online /remove-package /packagename:Package_for_KB2919355~31bf3856ad364e35~amd64~~6.3.1.14

If successful, use the same command prompt to run the following command:

DISM /online /cleanup-image /startcomponentcleanup

When that one finishes, copy/paste the fiollowing command:

DISM /online /cleanup-Image /restorehealth

When that completes, install KB2919355 again.

This error may appear anytime a Windows Update fails. To investigate possible solutions, we need to start with the specific error code.

We can do this by viewing your update history.

1. Swipe in from the right edge of the screen (or, if you're using a mouse, pointing to the lower-right corner of the screen and moving the mouse pointer up), and tap or click Settings.
2. Tap or click Change PC settings, and then Update and recovery.
3. Tap or click View your update history.

View failed update error code.

I cannot believe this is happening again!  This is SO frustrating!  Finally, the updates started installing fine and then today, it starts all over again.  PLEASE HELP!!!!!!!           

I wiped my system on my other computer and reinstalled everything. I don't seem to be having any problems anymore - also all downloads from Microsoft have had no issues so far.

This is probably because you already have a partial installation of KB2919355 which the new attempt is unable to overwrite. This results in the installation attempt being undone like you describe.

So do the following next.

Go to Programs and Features in Control Panel and click the link to "View installed updates".

In the next menu, copy/paste: KB2919355 in the Search field top right. If it's installed, it'll appear below and you can uninstall it from there.

If it's not there, close Programs and Features, right click the Start button and go to Command Prompt (Admin). Then copy/paste the following command and hit Enter:

DISM /online /remove-package /packagename:Package_for_KB2919355~31bf3856ad364e35~amd64~~6.3.1.14

If successful, use the same command prompt to run the following command:

DISM /online /cleanup-image /startcomponentcleanup

When that one finishes, copy/paste the fiollowing command:

DISM /online /cleanup-Image /restorehealth

When that completes, install KB2919355 again.

Followed these instructions, but it didn't work out.  It got stuck at the "restorehealth" command, at 40% for 6 hours.  I am letting it sit like that overnight to see if it does anything more.  By the way, this is an Intel i-950 machine.

Close the command prompt, re-open it and then run the following command:

DISM /Online /Cleanup-Image /RestoreHealth /Source:c:testmountwindows /LimitAccess

This command will use Windows files which are on your computer to repair the store. The /LimitAccess switch prevents the tool from downloading files from Microsoft's servers which is what the /RestoreHealth switch usually does.