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

We've seen this issue on at least 7 different machines here at our shop since May, 90% of the time, the following procedure will restore everything including your programs and files (and also install the latest build at the same time). Thought I'd share:

• Get a Windows 10 installation media (USB or DVD should both work), get the media creation tool here: https://www.microsoft.com/en-us/software-download/windows10

We're going to be doing a repair installation. While I mention this will keep your programs, files and settings, don't trust me, never trust anyone who says nothing bad can happen from toying with your OS. ALWAYS back up your stuff, back up your system as an image, do it often, do it regularly, and do it before you do this for sure. Stuff happens. 

• Boot to your sad, broken desktop with limited functionality so you see the error "C:\WINDOWS\system32\config\systemprofile\Desktop is unavailable." etc...
• Open a Run window = Windows Key > R
• Type "cmd.exe" and hit enter to run
• Insert your USB or DVD installation Media
• We need to determine which drive letter your installation media is since there is no explorer available, start by entering "dir d:" as d: is the first likely drive letter to be assigned, you'll look for an output that says "Volume in drive D is ESD-ISO", if you see that message you're almost home. (If dir d: does not return that message and a list of files, keep trying drive letter possibilities, dir e:, dir f:, etc., in order until you reach the one that is called ESD-ISO)
• Next, move to the proper directory by typing "X:" and hitting enter (Where X is the drive letter containing ESD-ISO you discovered in previous step)
• Then type "setup.exe" and hit enter
• The Windows upgrade program will then run. Since your network is likely non-functional, when it asks if you want to check for updates, decline, it will save you some time and a possible error message
• Make sure when it asks, you DO want to keep all programs and files
• Wait several hours (depending on your hardware)
• Wait some more
• It will likely hang for a long time at some percentage around 80, go ahead and wait
• If you're not done waiting yet, feel free to wait some more
• When it's done... Oh wait, it's not done yet, wait some more
• When it's done, HOPEFULLY you'll have your whole system back where it was with this nightmare of a botched upgrade installed.

We've not been able to nail down the cause in every case, but there is a pattern emerging in our experience, Avast antivirus software seems to be installed on a majority of the PC's with this problem. And an interruption in the upgrade process (power outage, system overheat, etc.) is a CERTAIN cause of this issue. 

We've also had a couple of machines where this process hasn't worked to restore the OS, I'm sorry if you're one of those people, but hope another kind soul will post here if they've had success where this failed.

Thank you so much for this info. I have a laptop that has swappable HDs that I use between work, personal and volunteer endeavors. I leave next week for one of my volunteer groups and began prepping the drive with all of the updates. Low and behold, the dreaded 1803 update provided the same problems that many here have described. Why it hasn't been resolved by Microsoft over 6 months later is beyond me. After perusing through all 46 pages of posts here, I went back to this post, followed your advice to the T and my HD is back in business.

Thank you again!

So glad to hear!  I got as far as turning my laptop on again and logging on as normal to recreate the initial error only to see my desktop but with a new error - "sihost unknown hard error".  I guess i need to find that thread now.  LOL!

Please watch this video:

https://www.youtube.com/watch?v=2-8gOC4BgYw

This involves the explorer command.  Windows + E isn't working for folks, which is probably sending people into panic.

This is where you download the official Microsoft ISO from.

Go here.

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

Read through the option that says using the tool to create installation media for another pc. Even though it is for the pc you are using.

(It is the 2nd plus sign under download tool now.) Follow the directions.

If you download the tool first to your downloads folder then open the downloads folder and right click the file for the properties. Click in the unblock box at the bottom of the properties page. Then again right click the file and choose run as administrator. It will ask where you want to download the file  choose your USB flash drive you have plugged in. Accept defaults if they are correct. The iso will download to your USB drive.

To install reboot pc with usb flash drive inserted. as soon as the pc is starting up (must be quick) keep on the F12 or (what ever your pc uses )key then choose to boot from usb drive once the boot menu comes up. Setup should start automatically.

 Hope this helps.

Thanks so much!  I used to be really good with this stuff, but after surgery for a brain tumor 10 years ago I'm just awful.  Working on it now... fingers crossed that I have enough space for the install.  Fortunately, I was too lazy to upgrade my desktop from 8.  It's tile city, but works.