Hi,
Thank you for posting your query on Microsoft Community.
I understand that you are unable to delete the system image. We will help you to resolve the issue.
This issue may arise when your computer is infected with virus or malware, I suggest you to run a full scan of your computer using Microsoft Security Scanner and check if it helps.
http://www.microsoft.com/security/scanner/en-us/default.aspx
Note: Any data files that are infected may only be cleaned by deleting the file entirely, which means there is a potential for data loss.
After performing virus scan, I suggest you to use Disk Cleanup from the below link to delete the files.
Hope the information helps. Let us know if you need further assistance. We will be happy to help.
Thank you.