|First make sure you have not left on your caps lock.|
If you had a password, how could someone get into it to change it?
If you strongly suspect this, you probably know who it was, try to force the issue with them and get them to admit it and tell you the new password.
This is your best answer.
No we cannot tell you how to crack your password. Many people come here asking us this in many different ways, some are legit, most are not.
There are ways to save your files and restore the computer to the way the factory shipped it. If this is what you need, explain yourself better.
If you contact the factory service and can prove your ownership, they may be able to help you with this.
You have to be a little bit crazy to keep you from going insane.