After update of my windows 10 I got problem Desktop is unavailable

So, there are a few software options out there, but I use one called Macrium Reflect (before anyone says anything, no I do not have any connection with this company!)

Basically you install this on the PC you want to protect and set it up on a schedule so that it creates a daily (or weekly or whatever you choose) "image" of your HD and either stores it somewhere else on your network or onto an attached portable hard drive. The image is basically a perfect copy of everything on your hard disk.

I use what is called a NAS (Network Attached Storage) which is just a big hard disk that connects to my network (so it plugs into the router), but you could just as easily do this by plugging a portable USB hard drive into the computer.

As part of first setting up the software you would also create what is called a "recovery disk" which is typically one of those little USB keys/drives. What the software does is copy some special files onto this little disk so that it's super easy to copy the image back onto your hard disk if something goes wrong. You only do this once, and then you just keep the USB key safe somewhere.

If something goes wrong such as has happened to people in this thread then you just put in the little USB key, and boot up your computer, most likely you need to press a certain key while you do this so that it boots from the USB key instead of your broken/corrupt hard disk and then the software copies the image from wherever it was stored back onto your hard disk so that you're then back to where you were at the time of the back up.

It maybe sounds complicated, but once you've set it up you can pretty much forget about it although I tend to just open the software and look at the logs in case it had any problems making the backup.

Macrium has a free version which has a few limitations and then various paid options to do stuff like make the back ups more efficient/smaller/quicker etc, but like I say, there are others out there which might be as good or better.

Yes, I don't know anything about taking an image of the HD - if you could explain in plain (non-techie!) english, I'm sure it would help some of us.   TIA.

this has worked for several people-hope you can get it to work for you....

Things you will need:

8GB or larger blank USB stick

a functioning Windows PC to use briefly

about an hour or two of spare time

Steps:

1. Turn on the problem computer.
2. At the blue screen, choose your language. 
3. Choose “Use another operating system”. 
4. Choose the second option, “Windows 10 on volume [x]” NOTE: Mine was the third option-above or below from the rollback option
5. Wait for the computer to boot to the desktop (if necessary, enter your password to login). You may have to wait a long time for the desktop to appear, while the “update” gets ready.
6. Once the desktop attempts to load, close any error message that appears.
7. On a functioning Windows PC, go to www.microsoft.com/en-us/software-download/windows10.
8. Click “Download tool now”. Disable any antivirus on the functional PC before proceeding to step #9.
9. Run the tool you downloaded, and follow the simple steps to create a Windows 10 installation USB stick (on your BLANK USB drive). The only option you should check is to make sure it is a 64-bit or 32-bit version. Your computer is MOST LIKELY 64-bit, and if you install the 32-bit version when you don’t need it, you’re probably going to have a bad time.
10. On the problem computer, right-click the taskbar, then click “Task Manager”.
11. Click “More details” so that you can see the menu bar. [fig. 4]
12. Click “File”.
13. Click “Run new task”. [fig. 5]
14. In the dialog that appears, check the box “Create this task with administrative privileges”.
15. Click “Browse…” if you look around, you can see all your folders & files-just leave them as they are & continue the steps.
16. Navigate to your USB drive and select “setup.exe”.
17. Run the file and follow the steps to “upgrade” Windows. Uncheck the boxes for “check for new updates” and to “help make this version better”.
18. Let the process run, which may take some time. Once completed, the computer should be back to normal, and fully up-to-date. You may need to re-login to your Microsoft Account.
19. While it is not necessary to remove your third-party antivirus software, we’d recommend that you remove it anyway, given that it likely caused the issue. Windows Defender is built in to Windows 10, is free of charge, and is quite adequate for consumer-level protection

Thank you so much for this fix, worked perfectly for me.

As you say, Nice to see so much collaboration towards an ultimate goal. 

Easy to follow instructions and worked first time.