When you noticed that the computer name had changed you should have stopped immediately. Changing the computer's name alters the SSID of the administrator, (the only person who can access an EFS encrypted folder in the case of loss). Once the SSID of the admin is changed then the ability to unencrypt the EFS folder is gone.

Now, if you put the drive back in the original box, (unchanged I hope), there is a linux boot disk that I have had success with that will set the administrator password to <blank>. I'm not at work right now where it is but I can hopefully get you the place to D/L it if you can't Google it. It worked perfectly for me getting into a Win2k server that I set up for being publicly available and outside the firewall that I promptly forgot the password for....