My lenovo R400 won't recognize my password when I'm trying to log in. How do I fix this?

Are you sure your password was with all lowercase letters? Are you sure that as you type each keystroke registers on the screen? Watch the screen as you type your password slowly and make sure it moves with each keystroke. A bad keyboard will cause a problem with your password. If all the above does not solve it turn off your computer, then turn it on and hit the F8 key repeatedly until you see an option that allows you to log into Safe Mode. Take the Safe Mode Option and when it boots up hopefully and depending on your operating system it will give you a log in for the Administrator and for the user which you forgot the password. Log in as the Administrator and hopefully you have not password protected it. Once you log in successfully go to Start/Control Panel/User Accounts. Once you are in User Accounts, select the user account that you forgot the password for and select the option to Remove Password. Then restart your computer.