Does the system show any sign of life when you try to boot it?

Yes, the power light still goes on and off as I press the power button.
All my data are saved personal data in my nextcloud and system settings in my rsnapshot. as personal data are synced with other laptop.
This hp625-fubar came new with a SuSE install 11 years ago. I gave it to a family member.
Then the video failed in warranty and it came back to me.
When the video worked again, I saw a windows installation.
So someone (This Family Member) put windows95 on It.
I did not return it to family member, but I put debian on it and used it myself.
However Hewlett Packard was more a Hewed baggage than a helpful notebook. The hardware is full of kinks which debian / devuan does not respond to.
So there was eternal trouble with the fan and the video chip with internal broken bonds caused crashes the last time. This caused the initiation of this thread.
https://github.com/TheAomx/HP-625-Linux-Fancontrol
A trial to repair the video chip resulted in complete darkness.
Now I took all removable items (WLAN card, 9GB memory , SSD, battery ) out of this brick and it will go the path of all electronics. back to the furnace.

BTW: The solution is a used Lenovo E460 which I bought on Monday. Together with a lexmark printer and other supplements 260€
The SSD with windows10 will be removed and this SSD put inside.
A fresh install of devuan chimaera is next. But that will be a new thread, when I put Devuan on it.

System FUBAR (video ATI RadeOn 4225 failed, no display. )

How badly failed is it?
Does the system show any sign of life when you try to boot it?
Does the display work if you try to boot off a live disk/USB stick? If not it might be a hardware fault.
Have you got another computer on the same network? If so does the faulty system respond to ping? Or come up far enough to SSH onto it?
Does ctrl-alt-f1 get you to a text screen?

You should get a login point... from there you'll have dpkg...

Boot into single-user mode and use dpkg -i to install the package.

You can then try to install the deb with dpkg --install FILENAME, if you can't boot or dpkg doesn't work, you can manually copy the appropriate file into the right location - you can get the file by opening the deb with any archive tool that supports "ar" format, then looking inside data.tar for the relevant file. (If you're using a Live USB to do this, make sure you've mounted the appropriate filesystem in a suitable location, and are not copying into the Live OS's filesystem.)

Also worth pointing out that, if you didn't also know the package name (e.g. if apt-file isn't installed or dpkg-query -S FILENAME fails), pkginfo.devuan.org allows search by file by changing "Package pattern" to "File pattern" - despite looking like text it is a drop-down.

devuan chimaera

Due to a crash libunistring.so.2 /usr/lib/x86_64-linux-gnu/libunistring.so.2.1.0  is missing

this is needed from various apps needed for maintaining the system.

aptitude (and similar maintenance tools) run into an infinite loop complaining about the missing file.

How do I reinstall the package (and maybe others) in rescue mode ?
apt-file search libunistring.so
libunistring2: /usr/lib/x86_64-linux-gnu/libunistring.so.2
libunistring2: /usr/lib/x86_64-linux-gnu/libunistring.so.2.1.0

rescue mode
no apt, no apt-get , no aptitude !

edit:
  no dpkg in rescue mode!
  wget relies on libunistring.so.2
  a multitude of packages rely directly or indirectly on libunistring2 !