Because it's system volume, Windows can't fix drive when is used. When you confim yes, next reboot of your computer will start CheckDisk (with confirmation). It will scan and repair your drive and boot into system.
The important question is: was your document really on the C: drive? -- <https://forum.pspad.com/read.php?2,79318,79327> PSPad freeware editor https://www.pspad.com
