Taking back ownership of files
Having problems with file security or did you just experiment and now you're getting access denied errors? No worries, you can take back ownership in most cases.
You can do this on the entire drive and reset everything but it will take a long time and could screw up matter even worse. Depending on where the access denied errors are occurring is where you need to reset your permissions.
Open Windows explorer and click on tools, folder options, view, and the at the very bottom turn off simple file sharing (uncheck 'use simple file sharing').
After finding the folder right click on it and click on properties. Now click on security. First try to simply give full rights to the administrator account. If you do not see the user name administrator or administrators then you will need to add that user by clicking on the add button. After adding the user, give them full access. Now click on advanced and then check mark both 'Inherit from parent the permissions entries...' and 'Replace permissions entries on all child objects ...' then hit apply. It may take some time to apply the permissions.
If you received a lot of access denied errors during this then you need to take back ownership. As long as you are logged ion as the administrator this is possible. While you are still in the advanced properties click on 'Owner'. Now select the Administrator(s) user and then check 'Replace owner on sub containers and objects'. Then click apply. Voila! You are now the owner. Keep in mind this can take some time depending on the amount of files.
Now go back and apply permissions in the Permissions tab as I stated above.