I experienced a complete failed Win10 upgrade even though Microsoft said my PC was compatible. Unfortunately it wasn’t and the Win10 upgrade hung at 70% complete. I had to use my windows 7 recovery disc to recover my PC after working with Microsoft support for over 10 hours trying to restore windows 7. I spent many more hours cleaning up the mess this upgrade caused me.
I recommend everyone check with their PC manufacturer to ensure your specific model and serial number PC can support Win10 before installing it.
You should make it a practice to back up your compute on a periodic basis as you never know when you might have a problem with your setup some day. Fans stop turning. Hard drives fail. Power supplies die.
And sometimes you get the BSOD from the OS just to remind you who is really running your machine. *grin*
System Rescue CD is a valuable addition for as-needed rescues of machines gone bad, and it comes with a ‘nix program called “partimage” that will make exact copies of any partitions on your HDD or even the entire drive so you can re-install everything to exactly as it was previously should the worst come to pass. It takes a bit to learn the command-line instructions to use it comfortably but I believe it is more than worth the effort.
It has already rescued many machines here over the years and I keep copies about in several places so I can grab one and perform a rescue whenever it becomes necessary. Love it. :)
Cheers!