thanks for the query. You are mostly right re the OS X version.
After rechecking via the serial no. I have found that I have a 13 inches A1278 model from early 2011.
One of the support sites suggests that it might be then OS X 10.6.6.
It could be even up to version 10.7.2 if it was a later model.
Thanks in advance.
boot into Recovery mode by holding down ⌘R as your MacBook Pro starts up. When the OS X Utilities menu appears on your desktop, select Utilities from your menu bar, and from there select Terminal. In Terminal, run the following command:
Follow its instructions, and your administrative user’s password will be changed accordingly. Exit Terminal, then select Restart from the Apple menu to reboot into normal mode. When the login screen appears, log in as your administrative user, and then reset your administrative user’s password keychain so that it won’t constantly ask you for your administrative user’s password when you need to do administrative tasks.
If you find that your administrative user is still parentally managed, you could reboot into Single User mode, and enter the following commands there:
/sbin/mount -uw /
/bin/rm -f /var/db/.AppleSetupDone
These should allow you to create a new administrative user, from which you should be able to reset your original administrative user to a non-managed state.
I have tried both options, but neither worked for me.
In the first option, there was no user account to select from.
And the second option has obviously removed the setup file, but it did not reboot into the setup assistant program afterwards.
After a short booting sequence/noise the Mac shuts off.
I am thinking of reinstalling the system...
Is there anything I still can try?