My account is is in the Administrators group; why can't I modify files under the "C:\Windows" directory?
2 Answers
Because Administrators cannot automagically edit all files. Have a look at the file fle permissions, and grant the "Administrators" edit permisions.
It depends what you want to modify.
Some files as Daniel said are protected and you will need to modify permissions, however, other files could actually be running/in a process and be locked from modification.
Please indicate the name of the file you are having problems with and I can try to help further.