Black screen with cursor

[status1]

My mother happened to stumble into this problem somehow and I am trying to fix it
The pc is a Lenovo thinkcenter desktop with windows 7 pro installed

It seems like this is a fairly common problem with no real cause with the only fix being to reinstall windows
So booting in normal or safe mode has the same results Just a black screen with cursor
Does anyone know what is causing this ?
How can different problems cause the same symptom ?
I heard some folks saying it's a hard drive problem which I kind of doubt because if the hard drive was bad it would probably fail to boot or it would freeze or crash at some point and also how is it possible that all hard drives fail with the same exact problem

The other theory is some kind of virus or malware but I haven;t heard anyone actually confirm this or know what virus is causing this

Some of the proposed fixes start with using the CTRL-ALT-DEL but unfortunately this is not working
with this problem

Any suggestions how I should start to fix this problem ?
I have a windows 7 boot cd but I don't want to loose my programs plus I would like to find out what is causing this in case it happens again or perhaps prevent it from happening again in the first place

One small clue which may or may not mean anything is that when I boot in safe mode normally the files scroll up pretty fast but with this problem it is very slow like maybe writing one line per second or two then scroll the screen up by one and write the next line

 

[status1]

Looks like I managed to make it worse
I tried a few thing after which now it's not even booting to that point
Now after bios it says No operating system
Not only that but when I use the Windows 7 instillation disk it doesn't even see the C drive
All it shows is the CD rom as the only device
How is this possible ?
The hard drive is recognized in Bios but after that it's invisible
I was watching a video where it mentions that for windows 8 it needs some driver for the hard drive controler in order to see the drive
Is that a possibility for windows 7 also ?

 

[status1]

Well since I had no options left I had to reinstall windows 7
Somehow the installation found the hard drive even though it was not listed during the setup
Unfortunately this does not explain what the cause was so it could happen again unless it was just an oddball virus
I guess I have to make backups and restore points from now on to make it easier to restore