Hello and thank you for choosing JustAnswer.com
Im very sorry to hear about the problem with Windows 10. You are NOT alone, and many folks have had many problems with Win10.
What you have described, is an install/upgrade loop, where the upgrade package keeps trying to run, EVEN after the upgrade was done.
A Glitch/Bug that is beig addressed by Microsoft, but they have YET to release a patch for it.
YOu have but 2 choices
1- Use the Win10 install Disc, or download to re-install Win10.
2- Throw it away, and buy a new PC.
Option 2 is probably not an option, so we will focus on option 1.
To re-install Win10 on a computer that does NOT boot to an operating system, yu will first NEED the Win10 Install package.
Download it from Microsoft, its free, and still available.
After that, you need to make the Win10 install package BOOTABLE (by burning it to DVD, or burning it to a USB drive), and then pop that in the faulty computer, and re-install.