Help with changing password on laptop

My power cord gave out on me and I had to order a new one. By the time it got here, the password to unlock the laptop had expired. I put in my username and the old password, then new password and it won't let me in. It says the username or password are wrong. They have been the same for 18 months now. I do not know how to get into my laptop. I don't need the darn password protection anyway. Is there a way to circumvent the process? I really need to get into the laptop, its been over 2 weeks and I don't know what to do. I am sure the username and password are correct. Please, please advice me as to what to do. Thank you.