Bought mini mac used no disk and start up password

If you have installer disk handy,

Versions 10.9, 10.8, and 10.7
Boot into the Mac OS X boot loader menu by holding down the OPTION key at system start

• Choose the Recovery drive to boot into recovery mode and wait until the "Utilities" screen appears
• Pull down the "Utilities" menu and choose "Terminal"
• At the command line, type "resetpassword" without the quotes
• Confirm the new account password, then reboot the Mac as usual

Versions 10.6 and 10.5

• Insert the bootable DVD into the Mac and restart or start the computer
• Boot the disk by holding down the "C" key at system start
• Select your language preferences and then under the "Utilities" menu select "Password Reset" (it may say "Reset Password" instead, depends on theversion of Mac OS X)
• Select the hard disk that the forgotten password is on, then select the username of the forgotten password, you'll then be asked to select a new password
• Reboot as usual from the hard drive, using your newly reset password as the login!

If you boot the Mac Mini from the system disk and go into Disk Utility you will be a able to resent the admin password for the computer.

Lost Acer admin password? Don't worry about it, you can reset lost acer admin password with Smartkey Windows Password Recovery Professional by the following steps,

Step1: Download Windows Password Recovery Professional from http://www.recoverlostpassword.com/products/windowspasswordrecovery.html.
Step2: Install and launch it to any accessible computer.
Step3: Use a blank and writable CD/DVD/USB to burn Windows password reset disk with the tool.
Step4: Boot the locked computer from CD/DVD/USB.
Step5: Start to reset acer administrator password with the burned disk.
Step6: Reboot computer and login to the locked PC without password.

Well you can reset your windows 7 password to log on the windows with the newly created password. And so many methods can help you ,such as the easiest way is use Windows Password Reset, or reset in safe mode ect.

Download Trinity Rescue Disk and use it to make a bootable TRK USB drive. You may have to change BIOS settings to allow booting from external USB drive. Boot from the trinity rescue disk, and use the "windows password resetting" feature to remove the password from your user account.

Could be as simple as you have the caps lock on, the password is case-dependent.

If not, you can reset your password by booting up the mac with the system disk (usualy disk 1 of the instal disks supplied) hold down the c key on your keyboard once it has booted up go to the menus and you will see a change the password item, use this to change the password. Once you have changed it quit out of the install disk and restart Hope this helps.

The only thing you can do is to reinstall the operating system from disk.

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Many thanks

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Here’s how to create an MAC admin account without knowing the current administrator password.
MAC Admin Hack

by changing the password from the instal disk you can get into the computer but you need your old password to open keychain. How did you lose authority in the first place?

You would need the disk 1 operating disk ,reboot system hold down c key as system is starting. When menu up, goto change password.