Choose a file system for C drive based on your demand and click “OK”. Insert CD/DVD into DVD-ROM or connected external DVD drive. Step 3. Step 1. : This way can also be applied to format C drive with Windows 10/8.1/8 installed. PS. Step 2. 1. The easiest way to do this is to boot from an operating system (with formatting abilities) via a CD/DVD/BD drive , flash drive , or floppy drive . Open File Explorer by double-clicking This PC icon from desktop and right-click C drive and choose Format option. Create a System Repair Disc. If you don't have a copy of Windows 7, 8, or 10, you can create your own disc and use it to boot then format drive C. Steps to format C drive with a System Repair Disc. The solution is to format C from outside of Windows, meaning you need a way to format a drive from somewhere other than your Windows installation. On Windows computer, you can format any partition except system partition in File Explorer or Disk Management when operating system is running. Step 1. Here you can confirm your operation and click “ Apply ”>“ Proceed ” to implement it. Right click the C drive and choose “ Format Partition ”. 2. You can also format C drive by making a System Repair Disc. Then you will receive an error message "Microsoft Windows.