If you are running - for example - Windows XP, 2000 or NT then the system will not allow you to make the changes you are trying to make unless you have administrative privledges.

If this is your personal computer at home and you are the main user you should be the administrator. Have you assigned a user name and password? Reboot (you have probably done this) If you get a sign on screen when you boot see if your name is on the drop down screen. Enter your password and sign on.

If you haven't been using a logon name and password the repair shop may have assigned one. Call them - most likely they use a standard name & password. Often it is (name) "administrator" and (password) "password".

Without more details it is difficult to analyze your problem.

Good Luck,

Norm