How to save C disk documents when OS is broken?

Boot into pe with a CD-ROM or boot into a U disk with pe, enter the pe, you can transfer out the important data on the c disk, then reinstall the system.

pe doesn't affect the c-disk, and won't use the files on the c-disk, so the best way to solve your problem is to enter the pe environment, back up the important data on the c-disk, and then you can install the system