Computers these days usually don't come with a Windows installation disk because you can download the iso and make your own. Yea, if your computers gone bonkers then you have to use a another computer to do this.
As I mentioned previously - download the Windows 10 Pro file and burn it to a DVD or make a bootable thumb drive. This should be the first thing you do. Do this on your working computer, but you knew that, right?Create installation media for Windows.
Click on the Windows 10 link and then the "Download Tool Now" button to download the iso file.https://support.microsoft.com/en-us/help/15088/windows-create-installation-media
You don't need to install Windows 7 first because you have the 25-character product key. Why not? Because you are going to do a clean install and the Windows 10 install will wipe everything off the disk anyway. Previously, Microsoft forced users to upgrade to Windows 10 before they could start fresh and do a clean install–which was annoyingly complicated and time-consuming. Now, things are much easier, since you can activate Windows 10 with a Windows 7, 8, or 8.1 key.
Next, you will have to burn the iso image to make a boot disk
. Every computer seems to handle this differently, you can Google "burn iso" and include the operating system you are using or download a free iso app like Free ISO Burner http://www.freeisoburner.com/
, install and follow the directions to burn a boot disk. (are we having fun yet?)
Part 3 - make sure the broken computer has a internet connection
Part 4 - turn on the broken computer. Don't think, just turn it on. Is it on now? That's a good boy. Open the CD drive and insert the boot disk you just made. Close drawer. Turn off computer.
Part 5 - Turn on Computer and boot from the disk drive or flash drive. How To Boot From a CD, DVD, or BD Disc https://www.lifewire.com/how-to-boot-from-a-cd-dvd-or-bd-disc-2626090
Part 6 - Enjoy the Windows 10 installation journey, it will take a while because the installation program will connect with the Microsoft Mothership to download updated files and drivers for your computer.
Here is your journey with pictures: How to: Perform a Clean Install or Reinstall of Windows 10 https://answers.microsoft.com/en-us/insider/forum/insider_wintp-insider_install-insiderplat_pc/how-to-perform-a-clean-install-or-reinstall-of/aef0ae63-2117-41ee-a8ea-4a3181625b08