Security - read only

Windows vista allows the change of file property ie. hidden, read-only.
Believing it would keep my files secure, I switched to read-only (in case
anybody tries to change anything).

That's the problem. I tried to 'unread'-only all the files but it just
doesnt work that way. Installing file shredder softwares also don't work as
it replies that the files are "in use and can't be deleted".

Now, I can't delete the items (even though using administrator access) and
also can't make any change myself (even though logged in using the same
account). How do I solve this issue? Reformat the computer? Thanks!

Security - read only