No profile picture or password box appearing . Acer nitro 5)

It's annoying safe mode isn't working, we will need to use the command prompt to solve this one.

Reboot into the blue troubleshooting screen again (shift and restart) hit troubleshoot advanced options, then click command prompt

This will then ask you to log in to an admin account, just your normal user should be fine

​type the following (explained step by step below, but these are the commands). Please read ahead and swing back round to this. Each command is one line so there are three comands in this bit

Now stop, is the above the exact same as this:

If it starts X:\ you are in the wrong place! Stop and re type the above three commands including the C:

If it is, continue, again each command is one line, so three commands:

What has gone wrong is the cache for the login screen has become corrupt, there are two databases in the above directory which controll the effect. What we are doing is moving them out of the way so windows doesn't see them. 

So step by step this is what the above commands do , as running commands blind is always eh 

1) c: 

This moves you into the boot directory from the system recovery directory, think of it like double clicking on a usb drive when you put it in

2) cd Windows\system32\config\systemprofile\appdata\local\microsoft\windows\caches

we are moving the files to the folder we just made. This will move two database files, and maybe some shm and wal files to the old folder. These will be re created on next reboot. 

6) exit
We er exit

So some answers to a few pre emptive questions :-

 - Why did this happen?
its a known bug in windows 1909 . as it arrived late in 1909's release cycle it was never fixed. 

 - Is there a way to stop it happening again?
When you are back on , try heading into windows update and mashing check for updates a few times. There is a new major release available which solves this.
 
 - is there a way without command prompt?
ish. Safe mode isnt an option here (which was why i asked that first), so your two options are a system restore / system reinstall, Boot the drive using an external adapter, or booting into linux to do the above. All of these are less easy than using the inbuilt windows recovery enviroment

 - Is this safe?
yes as long as you 100% make sure you are in C:\Windows\System32\config\systemprofile\AppData\Local\Microsoft\Windows\Caches. The databases are recreated on the next log in. It may take a few to 30 extra seconds to log in, dont wory, thats normal