Pc starts with white stroke what to do?

I have to get in few days of a friend of a few years younger is a PC Problem is when I turn it on, I have as in the picture so a white line of flashes. What should I do jz? I have the hard drive of my laptop installed in the PC because I had no other. Where is the problem? How can I solve it?

I thanked in advance for the help.

This line is called a text cursor and it indicates that some simple DOS operating system has been loaded and is waiting for input. Windows is apparently missing or not found.

Press F8 at the start.

You have to reinstall an OS.

Install an operating system, quite simply.

What does OS mean?

Operating system

OS stands for Operating System, ie operating system.

Do you mean when I turn on the PC and press F8 directly or when the cursor flashes

OK

What START do not you understand? Will probably bring nothing, if on the old plate is no Windows boot partition.