Windows 8.1 does not work synonymous with USB ISO file?

My buddy has complained that his laptop sometimes hangs.

I backed up his data and moved it to my PC.

Then I wanted to reset the PC with the Windows tools ect.

There it stood: could not be executed. It loads a bit and then mistakes.

I went to search for solutions and have already tried the CMD.exe but he does not find the file path.

I booted over the USB stick and also recognized the installation of Windows 8.1. Then I completely deleted his plate (all down) and then continued the installation. Up to a certain point, everything went wrong. Some files are damaged or missing? But have the win from Microsoft. 8.1 unpacked and pulled on stick. As a result, you can now do nothing more. When I start over the stick again, I get displayed that are still hard drives and files on it. However, he no longer recognizes an operating system. In other words, it starts with the prompt: Boot device not found and the possibility to get into the BIOS. What else shows everything like 'detailed' data.

I ask for help and possible solutions.

We would have USB sticks but no disks or DVD's

Once completely new please.

An ISO file, so a disk image can't start. Must be copied bootable to the USB stick. With Rufus-USB for example.

Do I have to do that before, so it should be empty for booting?

Which procedure do you recommend?

Please describe the individual steps.

Reload ISO and then again.