A couple of weeks ago my SSD was running out of disk space and my 3TB drive was not GPT-partitioned. So I decided to reinstall Windows 8 ( and linux.) Before I did that, I backed-up all my personal data. When I restored the data, I decided to organize the data and clean up things. While doing so, some of the files could not be removed. The reason for this was that I had 'dangling users' with ownership to these files. The next steps describe how to get rid of this problem.

When you right click the file or directory en select "Properties" and go to the tab "Security", you see an "Account unknown" with number behind it. This is the dangling user account.

When you click the "advanced" button, you can see the ownership and again it shows the dangling user.

By clicking the "Change" link (you need admin permissions), you can alter the ownership. Select the user you want to be the new owner.

Press the "Ok" button. Now you can select "Replace all child object permissions" (in case of directory). This way you regain the ownership for all child objects as well. Press apply.
Now select the dangling user account. And click "remove". Press apply again.
Now you are back in control of your file(s) again.