Ophcrack LiveCD 3.4.0 is a completely self contained, bootable version of Ophcrack 3.4.0 - the easiest and most effective tool that I've ever found to "crack" your forgotten Windows password.
For a quick overview of Ophcrack, see my complete review of Ophcrack 3.4.0.
Ophcrack is a free software program that recovers passwords so the first step you'll need to take is to visit Ophcrack's website. When the Ophcrack website loads as shown above, click the Download ophcrack LiveCD button.
Note: Since you obviously can't get into your computer right now because you don't know the password, these first four steps will need to be completed on another computer that you have access to. This other computer will need to have access to the Internet and the capability to burn a disc (like a CD, DVD, etc.).
Another Note: The instructions I've put together here walk you through the entire process of using Ophcrack LiveCD to recover your password. If you're a little nervous, it might help to take a look at this entire step-by-step guide before you actually get started.