defaultuser 1 after last windows 10 uptdate: not able to start my computer

Check if you are able to log into the account from safe mode.

At the sign in screen, do the following:

Hold down the shift key on your keyboard while clicking the Power button on the screen.
Continue to hold down the shift key while clicking Restart.
Continue to hold down the shift key until the Advanced Recovery Options menu appears.
Click Troubleshoot

Click Advanced Options

Click Startup Settings
Click Restart
Press (4) to Enable Safe Mode
Wait while Windows 10 starts in safe mode.
Log in

If that does not work...

Hold down the shift key on your keyboard while clicking the Power button on the screen.
Continue to hold down the shift key while clicking Restart.
Continue to hold down the shift key until the Advanced Recovery Options menu appears.
Click Troubleshoot
Click Advanced options
Click Command Prompt

At the command prompt, type:
net user administrator /active:yes

Hit Enter

Close command prompt, restart, then try signing into the Administrator account.

Try signing in again.

Hi, 

thank you for trying to help and answer so quickly. I tried both solutions again and again, but it did not work. 

I also tried "go back to the previuous version" but this didn't work either. 

I tried starting with windows 10 on volume 2 : same defaultuser 1 appearing. 

this is really frustrating.

Maybe this would helpt you to help me: 

I tried again the comand in the comman prompt, and it tells me: 

the syntax of this command is

NET USER
[username [password | *] [options]] [/DOMAIN]

      username {password |*}/ADD [options][/DOMAIN]

      username  [/DELETE][/DOMAIN]

      username  [/TIMES:{times|ALL}]

      username [/ACTIVE:{YES|NO}]

I also tried to get a list of the users by typing: net user

and the prompt gave me this answer: 

User accounts for \\

--------------------------------------------------------------------------

Administrator               DefaultAccount                    Guest

WDAGUtilityAccount

The command completed with one or more errors

I tried these 3 solutions:

net user[<defaultuser1>[/delete]]

The system cannot find the file specified

net user [<defaultuser1>[/delete] [/domain]]

The system cannot find the file specified

net user defaultuser1*/domain

the syntax of this command is

NET USER
[username [password | *] [options]] [/DOMAIN]

      username {password |*}/ADD [options][/DOMAIN]

      username  [/DELETE][/DOMAIN]

      username  [/TIMES:{times|ALL}]

      username [/ACTIVE:{YES|NO}]

I'm only a R Coder, I don't understand what I have to specify in this language. For example, I don't know if I should specify a domain, and then what sort of a domain?

etc...

I would be very happy to get help, I need this computer.

Thanks a lot!!