Even though you have administrator rights under your user account, you are not logging on as THE administrator. When you start the computer and are presented with the welcome screen (you DO get the welcome screen requiring password, right?), you need to press CTRL+ALT+DEL twice to bring up another screen which allows you to TYPE the word "Administrator" in the username and then either type the password for that account or just click OK (leaving the password blank). THIS will log you in as THE administrator, not just a user account with administrator rights. There is a HUGE difference between the two types of login and you need to be logged in as THE administrator to access registry keys.
If you do not see the Welcome screen when turning on the computer, you have not set a password for your user account (not very safe) and it will automatically log you in under your user account. To get to THE administrator account, you will need to boot up in Safe Mode.