Inaccessible files from deleted admin account

[Tycho1214]

OK, I have a problem here that is driving me utterly insane. I've recently had a problem with another computer in the household being used by another user. I don't know how exactly he accomplished this but this user has apparently created another admin account on the computer, which he then deleted via Administrative Tools > Computer Management > Local Users and Groups. The problem is, there are folders and files that apparently belonged to the deceased account that can not be removed - I am given an "Access Denied" message whenever I try to view the folder in question. I don't know terribly much about this, and he seems to be as incognizant of what exactly he has accomplished. I need to find some way to remove all these folders belonging to the extinct administrator account. The aforementioned user who caused all of this has suggested formatting the hard drive completely, the practicality and merit of which I doubt, particularly since a reinstall of Windows will invalidate the license.