Factory reset Mac Mini

I was given an old Mac Mini but it boots up to a desktop but when I try to do anything it is asking for a password that no one knows. I would like to do a full factory reset/wipe but no key combination I have found on the Internet seems to give me the Recovery app. I have tried Command-R, Option-Command-R, Option-Shift-Command-R at boot up, it acts like there is nothing there and goes straight to the desktop. These options are supposed to take me to the Internet to reinstall from there. THe Mac Mini is on the Internet. I have tried reinstall Disks and USBs that have OSX Snow Lepard, Mountain Lion, Yosemite, they all say it is not for this MAC. in the About this Mac section is says its Model identifier is MacMini 1,1 and on the bottom it says model A1176. Where can I find /download the correct bootable USB/Disk to do a factory reset?

Any help would be appreciated, I want to wipe it and donate it instead of e-wasting it.