Use a system File Check grom your Hard Drive
First make sure you have Folder 1386 in C: Drive,
Start, Run, 'regedit', OK.
Backup the Registry in case of trouble: File, Export (to a place of your choice).
You will see various entries here on the right hand side. The one we want is called:
It probably has an entry pointing to your CD-ROM drive, and that is why it is asking for the XP CD. All we need to do is change it to:
Simply double click the SourcePath setting and a new box will pop up allowing you to make the change.
Now restart your computer and try scannow sfc again!
Credits to a link posted by VoG™