Quote:
How to backup data from pc which don't have a os?
I guess your PC don't boot because something is erased in the very early booting step of the HDD. repairing this kind if thing is not for faint, it is an activity for expert.
You need a deep understanding on how the HDD is used by the PC BIOS to boot the OS.
The tools you need will allow you to do things that go against what standard tools allow you to do, there is no safeguard, that is why you have to know what you do.
The first step is to make a backup image of the HDD. It is an exact copy of HDD, no matter the contain. So that you can recover from a wrong operation.
Then repair what is broken or repair enough to access data.
Then backup your data.
I used to use:
Ultimate Boot CD - Overview[
^]
as a collection of tools.