You can try clearing the password via the Administrator login, if your machine has one.
1. Log out and reboot your machine.
2. When the machine starts the reboot sequence, press the F8 key repeatedly.
3. Select Safe Mode from the resulting menu with the arrow keys.
4. The machine will continue booting, but the Windows desktop will look different. You won't be able to see the Internet, for instance. Log in as Administrator. Administrator often has no password.
5. Click on the Start->Control Panel menu item.
6. Click on User Accounts.
7. Click on your regular account.
8. Click on Remove the Password.
9. Finish up and reboot normally.
Good luck.