Hit the windows key plus r and then type in netplwiz. Untick users must use password at the top and then click ok. Enter your password on the next screen that comes up and that is it.
If this is for a Microsoft account and you've been using a password that has more than 16 characters, you would only enter the first 16 to be able to sign in.
I have never needed a password before when I switched on my computer. When I logged on to windows 8 I was asked to create a password, I did not put anything in and pressed return, thus I was not asked again until now and somehow I have created one, thus have to enter a password when I switch on. I then tried to do the same again leaving it empty.