I mainly run into this when I’m using a server core install, but this works on pretty much any version of Windows. The only caveat is that you need to be an administrator on the system.
Of course, you need to run an elevated command prompt as well.
Just enter the following, and you’ll be prompted to enter the password and confirm it.
net user %username% *
You can also run the following command, which specifies the password:
net user %username% %password%
So, if BoDuke wanted to set his password, he would enter:
net user BoDuke *
or to specify a password of “GeneralLee4Life!” he would use:
net user BoDuke GeneralLee4Life!