Command Prompt Windows 8

I'm running a MacBook Air osx 10.8.4 with Windows 8 (32bit, so I presume Bootcamp 4.0). Windows suddenly stopped recognising my password (don't remember changing it!) and I need to reset it. Didn't do a password reset USB or sign up for a Microsoft account. Trying to work Tim Fisher's hack to reset password without having to buy 3rd party software.

I can access Advanced StartUp Options/Troubleshooting/Command Prompt but Command Prompt will not let me type any commands. All I get is a dialog saying I have to logged in as admin to make commands and so it asks for my password again - round in circles.

I've also tried going into Safe Mode with Command Prompt, but as soon as I select that the computer just goes into Restart and goes back to Mac OS.

Any ideas?? Would be much appreciated.

Cailin