Did this with 2 different USB thumb drives.

Tried to create a bootable USB on a Windows device using Transmac and another tool that's name escapes me.

When I get as far as restore I'm challenged for the admin password which I don't have so can't continue with this Then tried to create a bootable USB disk using Disk Utility on the Mac. I believe this is the latest version supported by the device.

Found and downloaded an El Capitan (Mac OS 10.11) image.Can't see a recovery partition, is this why Command - R does nothing? Each time it just boots straight into OS. Tried Ctrl - R, Alt - R, Windows - R, Shift - R, none of these work. What I've tried (I'm using a Windows style keyboard). I'm assuming my best option is to try and wipe the device. I've spent all afternoon trying all the different options I can find and can't get anything to work.

I then asked the guy I got the mini off and he cant remember what he set it to. I tried the usual basic things to no avail. I was trying to set up screen sharing so I can remote into the device and when I attempted to secure the VNC connection with a password, I was challenged for an admin password. When the device boots it goes straight into Mac OS, no login challenge. It currently has 10.6.8 Snow Leopard installed. I believe the device is the late 2009 2.26GHz model. He wiped the device before he sold it to me. I've only just got round to trying to set it up. I bought a second hand Mac Mini from a friend a couple of years ago.

Reset mac mini password