Guest system in Virtualbox keeps booting from a certain point how to fix?

Question

virtual box

Tell me, such a problem:

I start a virtual machine (windows server 2012), the state is loaded in which it was approximately at the time of installing the guest system.
Next, I create a test.txt file on the desktop, reboot - and the system starts again and this file is not on the desktop again. The hard disk file (.vdi) with this virtual machine lies with the modification date as of 07/11/2018

It seems that VirtualBox cannot write to the file of this virtual machine. However, everything is right and there are no errors at startup.

Tell me how to be?

I put a bunch of programs and a lot of important things on the virtual machine for several hours, rebooted it - and as if nothing had happened!!!

VirtualBOX version 5.2.6
Mother OS: windows server 2012
Guest OS: windows server 2012

ps when I downloaded programs to the guest system, the file C:\Users\Administrator\VirtualBox VMs\windows 2012\Snapshots\a lot of symbols.vdi grew,
however, after a new start of the virtual machine, it is cleared or its size greatly decreases and starts to grow again.

ps deleted this file, the system does not start at all,

what's wrong here ?!

Answer 1

Look at the properties of the disk through File> Virtual Media Manager , if there is Unchangeable , then all changes will just be constantly rolled back.
And return the snapshot back, for example, through the folder properties - previous versions.