I used to back up windows computers by booting off a linux CD and copying the entire disk to another disk using the "dd" command.
You can also just boot up from a CD/DVD. I prefer Knoppix, (linux) personally, and running from it, leaving the HD untouched, or install onto a hard disk. Running from CD/DVD is what the Tails distro does. Since the OS is on DVD, and parts of it are only temporarily in memory, it can't be corrupted by malware.
There's also a "System Recovery" linux CD that will let you mount the windows disk and perform whatever you need to do with that file system.
It has been a while, so these are just from memory.
I make it a policy to use "Super Duper" on macs to make a bootable image of the system disk now and then.
It's free to make clones, but not incremental copies, so it just copies the entire disk each time.
There's also CCC, but I don't use it. Must be ones for windows.
Too late for you? Then just rescue your files.
I also like to put all my important files on external disks anyway. $70 or so for a terabyte of SSD. By using sneakernet, you can transfer a terabyte in a few seconds! Unplug and plug into another system.
P.S. you can get a bootable linux CD from the net (knoppix.net) and burn it on another machine, obviously or copy to USB drive using the recommended tools. Or, when I hit the bookstores, I'd get a bootable dvd in a magazine.
🍀🍀🍀 AND GOOD LUCK 🍀🍀🍀