This is done by a very strange way, which is explained the movie here. https://www.youtube.com/watch?v=xXFV1w-8jww It looks strange but it worked fine. The movie was for a normal user but not admin. but it worked for admin too. it was literally like a charm.

This is how it goes.

Password Change

1. power on the computer.
2. Abrupt the starting-up win7 by Ctrl-Alt-Del. -> immediate shutdown.
3. when restarting, win7 asks for repair boot up. select it.
4. from here it takes abit.
5. Not repair.
6. view problem.
7. scroll until the very bottom. click the bottom line.
8. text editor comes up.
9. try to save it. then a window comes up for saving.but we can use it for not saving but for file maninpulation.
10. Go to localdisk:\Windows\System32
11. find sethc.exe. change the name sethc0.exe.
12. find cmd.exe. copy it. rename it to sethc.exe.
13. restart windows7 normally.
14. select user. in this case admin.
15. Press 5 times shift! very strange...
16. command line window pops up.
17. net user "username" *
18. Then password change procedure starts: input your password twice.
19. close the window. Login with the new password! Done!