I would create a bootable pen drive that would boot some form of Linux, change bios settings to boot from pen drive, use Linux to access system drive, then boot to Linux. Then mount the system drive as a linux drive, and change something on that drive that I can invoke by typing a lot of shifts ofr whatever into the login prompt instead of logging in to be a (privileged) command prompt (carefully saving the original), then boot again from the original drive and invoke that, then use a net user user_name * /domain command to change the relevant password, then login and restore the original of the thing I overwrote with command prompt. Of course to do that you need a machine with internet access to download something to create a boot drive if you don't already have something suitable on a machine to which you have access.

Google "windows 7 password recovery" and you should find detailed instructions for doing this (plus a pointer to a a boot disc generator for a suitable linus distribution, which you will of course need) amongst the fiirst half dozen results. Don't ask me for detail - I don't remember it, because it doesn't happen often enough to be worth remembering the detail as opposed to the rough outline so that I know what I'm looking for (I have done it, for a windows 7 machine, exactly once).

Have to admit I was somewhat surprised that Windows 7 was that insecure.

edit: and of course even more surprised at insecurity implied by method 2 above! ANd maybe method 3 implies total absence of any security at all?