Windows.old Folder Won't Delete

All went well and I feel my computer is working better now than it ever did. I did add a new asus mother board, a quad core processor 3.27, doubled the Ram, and put in a blue ray burner.After the upgrade was completed I waited for almost a week to make sure all was working well and then set out to delete the windows. old file. I did as was suggested and did it through disk cleanup. All looked like it was cleaned until I went into my C drive and see that the Windows.old folder is still there. I can't delete it. I shows that it does the files do not exist on C: windows.old but the file is still there. There are three folder but nothing in any of the folders. How can I delete the foler windows.old. I've tried everything suggested but can't seem to find a way. I even went into the registry but can't find anything.