here are step wise.

1> make a bootable pendrive with which windows os need to reset.

2> insert into usb port and boot from pendrive

3> click on repair

4> click on Command Prompt

5> select your C: drive

6> use this command

cd \Windows\System32\

ren sethc.exe sethc1.exe

ren cmd.exe sethc.exe

7> now remove your pen drive and boot your PC from HDD

8> when you see user and password screen.

press shift keyboard button 5 time.

after that you can seen this screen

9> now run this command

> net user (this command for see all users in your pc)

> net user (your username) * (example net user administrator*)

> then put new password