asini27 Said:
"[...]my question is how can I unlock the Users and Group Preferences in the system preferences? I have use my administrator's user name and my password but it won't let me unlock it. What can I do?"
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Strat Here:
Reset the NVRAM or PRAM and then reset the SMC, of your Mac. Sometimes, changes are made to your system, and then settings (i.e. for the keyboard) become manipulated, technically. So, when that happens, reset these to get things to operate as they should.
If Neither Reset Works...
Use Safe Mode:
Also, try booting into Safe Mode (Hold Down the Shift key upon boot). While in Same Mode, create a new administrator, that you have another Administrator User to use.