Houston we have a problem... bad password

I will give you a little bit of the low down to start with, we have recently purchased 20 Asus T100t tablets for our workplace users, they all came with the pre-loaded windows 8.1 installed however as this was only the standard version, one of our technicians set these all up and then upgraded them to our own image build.

the problem is that the technician has now left and it turns out they only put the image on to 19 out of the 20, the last one still has the standard build with a standard user account setup, Which none of us know the login for.

Can anyone advise me on how I can reset this tablet / laptop to factory settings so that I can create a local account and then put our own image on? We have tried many different password combinations, however none of them work and we are unable to get hold of the technician that has since left, leaving no detail of what the password may have been.

Any ideas people? The only options I get is with a password hint "jj" and the reset password link, which doesn't work as no forgotten password disc was ever created. I know prior to windows 8 I could have gone in to advanced startup options by using the F8 key during boot and used command prompt to reinstall Windows, however with Windows 8 I cannot find an option for this without already being logged on?

Thanks in advance for any help anyone can provide.

Perfect, solved it