Caps Lock might be on
It’s well known that the Windows password is case-sensitive, which means that the password your type in every time must accord with the one which you created first time. If you have accidentally pressed Caps Lock, then you’re inadvertently typing your password in all capital letters. So, please make sure that Caps Lock is off before typing your password again.
You might be typing the wrong password
If you can't remember your password, you need to reset Windows password, with an administrator level account or a password reset disk.
Y ou might be trying to log on to the wrong user account
If you have more than one user account on the computer, make sure you're logging on to the account that matches the password you're using.
Your password may be reset or changed by an administrator
If your computer is on a network, a network administrator has the ability to reset your password. If you think this might be the problem, check with your network administrator. If your computer is in a workgroup, anyone who has an administrator account on the computer can change your password. So, make sure if your password is changed or removed. If so, you need turn to ask a password reset disk or Windows password recovery tool for help.