I have an older Mac Mini (running a 1.25 GHZ PowerPC G4) from 2005. I had not used it for some time, but now want to use it as am HTPC. But I can't upgrade the software because I have (1) forgotten the root password and (2) lost the old boot disk. I don't need any of the old data, but would like to start over. It's running 3.9 and I want to upgrade it, but can't because I don't know the password. I do have an old MacMini 10.4 disk (from a computer at work), but it won't boot with this computer. What can I do to get this running again?