OS X Lion server software

Thanks to anyone who can help there. I am trying to resuscitate a Mac Mini running OS X Lion server software. It's been in storage since Feb 2011 when a big earthquake here wrecked our offices, and no-one at work can remember usernames or passwords, and the paperwork/IT equipment where they and the software serial number etc are recorded is also inaccessible after the quake. I followed workaround instructions thinking I could set up a new Admin user by deleting the AppleSetUpDone file within the root structure, but I didn't realise that I would have to enter the server software serial number etc to do so. After lots of phone calls I think I might know a username/PW combination that will work, but now can't find a way to either reinstall the deleted AppleSetUpDone file so startup runs as normal, or get into the Recovery disk where I was hoping to find the server software serial number (command-R doesn't seem to work). I can call Apple Support after the public holidays here but thought I'd try to solve it myself first. Thanks heaps for any help anyone can offer.