This page documents how to reinstall Microsoft Windows without losing Ubuntu.
If Ubuntu is installed the standard way (outside Windows)
- Backup your documents on an external disk (or DVDs...)
- Reinstall Windows
Restore GRUB (eg via Boot-Repair)
If Ubuntu is installed inside Windows (via the Wubi installer)
- Backup your documents
- Backup the wubi files (generally located in C:\ubuntu\disks\)
- Or reinstall Windows, then reinstall Wubi and restore the Wubi files.