OK, the log on password needed to access your user account.
You may reinstall your operating system. (cheap but may not be safe for your data)
You may go to a computer shop with a proof of ownership and have them do a password reset. (will cost you but should be safer for your data)
Before going further, and regardless of what you chose to do, you need to backup your files. Using a live CD or a console from the install disk, copy your data to an external drive.
If you have more than one drive installed, the data contained on the non-OS drive(s) are safe and don't need to be copyed.
DANGER!!! If you encrypted your data using BitLocker, those will be FOR EVER impossible to recover! The BitLocker key is derived from the motherboard serial number, BIOS version, drive serial number, VOLUME serial number (WILL change if you reformat), some user supplyed password and some other factor(s). Each BitLocked drive will have a distinct key. Part of the key is kept in a volatile area of the BIOS memory and can get lost if you unplug and remove the motherboard battery. If that part is erased, it CAN'T be recreated.
Electro, May 2012